Actually I have a list of 45 original articles waiting to be written by me to be posted on here. But yesterday I stumbled upon @scrooger and his Transformation blog thanks to @joanaltres

So my first article on steemit goes out to @scrooger, who you can see proudly showing himself at day 30 of his life-changing transformation, to support him in his endeavour of leading a healthier lifestyle. This is so very inspiring that I just had to postpone all of my planned articles about topics like psychology, philosophy and the nature of all kinds of things to help him with getting in shape, since he has developed such a great motivation but seems to not have too much guidance on how to go about training in the gym. My 15 years of experience in doing body-shaping (I like this terminology better than body-building because I am not into bulking up but rather about getting in shape) might help him and probably other people to get to the goal they have set for themselves.
Not that this only adresses what to do in the gym at the beginning, once you have already built up the motivation to do it.
Anybody else at another stage of training can leave a comment with any question about training and I will answer it in the most detailed way possible to help them as well, if that occurs.

Why you should build some muscles for the purpose of loosing weight

Muscles are more metabolically active. This means, the more muscles you have, the more calories you burn throughout the day even when not exercising.
Your body also looks better, when there is not just less fat on it, but also has some muscles under the skin to give you some tone.
Also, when you do weight-training, you body burns calories long after you have finished your workout.
Lastly, muscles affect your hormone-balance. Fat-tissue produces estrogen, which increases the body's fat storage capabilities. Muscles increase the level of testosterone, which increases the ability of the body to burn more fat.
For the girls that might read that: Don't worry, building muscles won't turn you masculine all of a sudden. Your body will never produce the amounts of testosterone a male body does, but still you will benefit a lot from trying to build muscles. Due to the generally lower level of testosterone you will also never be able to build the kinds of muscles a man can, so don't worry about looking bulky within a matter of even years!

So let's begin!

1. Training-Frequency

When it comes to going to the gym for weight-training, there is the general rule of going every second day. When you excert your muscles you should give them a rest of around 48hours before adressing them again. This rule can be bent though by designing a workout-plan in which you don't hit all the muscle-groups in every training (that is called a full-body workout). So there are ways in which you can go weightlifting every single day. But these designs are not meant to be used by beginners, because they don't need to push every muscle so hard in one workout to provide a sufficient stimulus, thus it wouldn't make sense to split the muscle-groups up into training them on different days.
So, for a beginner it is generally recommended to do a full-body-workout every second day leading to training 3 to 4 times a week.
In the course of this article I will lay out the optimal beginner-full-body-workout.
This rule of 48h of rest only applies to weight-training though! You can do cardio every day!
So if you are so motivated to do sports every day, you can also do it with a full-body-workout every second day and on the days in between you can hit the treadmill (or jog outside), get on the bycicle, swim or get on a rowing-machine.
If you have no definite preference for any of those cardio-exercises, I would recommend you to switch between all of those actually, depending on wether it is possible. Not every gym has a rowing-machine and maybe there is no pool in direct proximity to you. But this leaves you with the possibility of being more flexible, do sports outside if the weather is nice, etc.

2. Rest-days and deload-weeks!

Even if you are so motivated, that you want to do sports everyday, taking a day off once in a while is absolutely obligatory! You should not train more than 6 days a week and whenever you feel like you are really loosing too much energy for the daytime activites, take a day off to rest. This is very important for your nervous system, so you don't burn out. Listen to your body!
You will definitely feel, when you need to take a day or maybe even more off. But don't confuse it with lazyness. When you have slept in, slouched on the couch or just had very little physical activity, your cardiovascular system is down and your parasympathetic nervous system is overactive. This might come off as being tired but actually it is just your body being shut down and you will greatly benefit from getting some physical activity!
It is also recommended to do a deload-week every 4-6 weeks of training progressively. This means, that you should still do your workouts but simply modify the intensity of them down by around 50%. Meaning, you will just do half the sets of exercises you are usually used to doing or go jogging (or other cardio) only half as long as ususal.
This also prevents you from burning out, which could result in a way longer break being necessary to be taken or even losing all of your ambition to do sports at all.

3. How long should a good workout take?

When you do strength-training, it should never exceed 1 hour! How you can manage that I will show you in the following chapters. But why, you ask? Actually after 45minutes of excessive training, your body starts producing a greater deal of cortisol, known as the human stress hormone. This leads to more muscles being burned, inflammatory reactions and lots more. It is a counterpart of the beneficial testosterone. So it is way more effective to do a shorter and more intense workout than training hours on end.
Cardio is another matter here though. You should try to get to at least 30 minutes for a normal low intensity steady state training, like jogging at a normal pace. And you can bring that up to running a marathon, if you want. But take into account, that the longer you do cardio, the more rest you will need afterwards. So it may be more effective to run 3x for 30minutes on 3 consecutive days, rather than running 1 hour and then having to take a break for 2 days.

4. Training efficiency

Between sets of exercises it is recommendable to take short breaks for your body to recover from that work. This is a crucial point! You see many people chatting, using their smartphones etc. in between sets, which leads them to take breaks of many minutes before doing the next set. Don't do that!! You should always keep track of your breaks with a specific app or simply a stopwatch. If you take a break of 5 minutes in between every set, you will never get done with your workout and it even loses effectiveness! The shorter you breaks, the more your heart will keep working and the higher also your hormone-levels. Aim for 90seconds breaks in the beginning and over time try to get them down to 60 seconds. If you lift weights that are quite heavy for you, you might want to go up to 2 minutes breaks, but try not to exceed that. This leads me to the next point.

5. How heavy should I lift and how many repetitions should I do?

There are many different opinions on this issue, especially when it comes to beginners. The most important part about the number of repetions is, that their count is not the most important part about them. What is more important is, that they are executed correctly. You should stop a set, when you realise that your form gets worse and you don't have the weight fully under control anymore. You don't want to hurt yourself and you don't want to accustome yourself to doing bad movements just because you want to do 10 instead of 9 repetitions of an exercise!
Generally I would recommend you to pick weights for each exercise with which you can perform 10-15 quality repetitions. This can take a while to figure out, not everyday you have the same power etc. But it is extremely important to start with weights that are rather too easy for you to life than at the maximum of what you can do 10 repetitions with. That is because you want to focus especially on doing the exercises correctly in the beginning! You have to learn them like a dancer practices a new move or a musician practices a new song. Slowly and highly concentrated.
So test out what weight you can work with properly and take your time to learn the new movements.
But more importantly, stop a set, when you can't perform it correctly any longer!

6. Progressions

Try to increase the workload every week a little bit. Especially in the beginning, you will see real jumps in strength due to your body developing the coordination to execute them more efficiently. So don't just stick to one weight forever but try to do a little heavier weight every week even if you can do a couple less repetitions then.

The allround-full-body-beginner-workout

So now, since I have covered some of the important basics on hitting the gym, here comes the in my eyes optimal workout-plan for beginners. I will first describe it and in the end paste an excel table which you can carry with yourself to the gym.
Most training-routines for beginners are packed with machine-exercises but they are not as effective for beginners as directly training with free weights.

The exercises

You will start with two exercises for the lower body. The Front-Squat and the Deadlift.
Sadly, I can't find good pictures of those right now. But please make sure that you check out some videos on youtube on how to perform them correctly.
You will warm up for them with 2-3 sets of low intensitiy (Start with the bar alone and add a little weight with each warmup-set) and low repetitions (not more than 10 needed). You don't need to take a break of more than a minute in between warmup-sets.
So first, you will do 3 sets of frontsquats for warmup and then 3 sets of front-squats with the chosen weight for the day. Then you will do the same with the deadlifts.
Why start with leg exercises? Because they not only bring your heartrate up more than any other exercise, but they are also so intense, that you hormone-balance will be influenced very positively by them.

After those leg exercises, do two chest-exercises. I recommend you to do push-ups and dips. But only if you manage to do at least 10 pushups already. If not, pick the benchpress, because you can start easier there.
You will here do only one round of 2-3 warmup-sets with either pushups (do half of what you think you can do in each) or the benchpress. After this warmup-round, go to the dips-bars and perform 3 sets there. Then 3 sets of push-ups/benchpress.

After those chest-exercises, do two back-exercises. I recommend you to do either supported pull-ups with a machine that take weight off for you, or maybe you have those rubber bands, which you can hang your knee into so it makes it a little more easy. If that is both not available, there is another option: Grab the pull-up-bar and jump up so that you are on the very top - then try to let yourself go down in a slow motion and very controlled. This might be extremely hard in the beginning, but for this exercise it would also be okay if you only manage to do one or two repetitions. The other back-exercise is the row. If available, do it on a sling-trainer / TRX and if not, with a barbell. First do 2 sets of warming up with rows, then try to get as far as possible with pull-ups and then go hard on those rows again.

After that, do a shoulder-exercise. I recommend you the military press, but you can also do a shoulder-press with two dumbells. Do only one warm-up-set with a lighter weight here but still around 10 repetitions and then pick a little more weight and do 2 more sets with that.
In the same fashion you will follow that up with curls. I recommend you to start with dumbell-curls in both hands simultaneously.
And last but not least, you can do some training for the abdominals. I recommend basic crunches and criss-cross, to attack both the rectus abdominis but also the obliques. Do as many repetitions and sets as you want for them. Why do the abs come last? Because you need your abs to stabilize you in many movements. Weakening them beforehand would endanger you to perform worse in the other exercises. Plus, you need lots of energy for every step in that training plan and when it is designed like this, you have the optimal power-levels for all of them, not having drained yourself to early.

The cheat-sheet for the training routine

This plan will take you around 50 Minutes to execute.
Fill it out for every day, unless you can remember it mostly, so you can keep track of how many repetitions you were able to do with the picked weight.
The (WU) means the warm-up sets, which should also be noted down. Remember, do 2-3 Warm-up sets before the first heavier exercise, of which you then do 3 sets or maybe even more from time to time.
In the first week you can reduce it down to just the warm-ups sets to experiment with the weights and just focus on doing the exercises in a correct form.

I hope you can put this to good use. I am so looking forward to see you develop further along your 100days challenge and hope I was able to make some contribution to this.
There could be a lot more for me to write about all this, but this took me way longer than I thought it would and I am running out of time now... There will probably be edits, if I remember something important that I wanted to share with you but forgot.

If anybody has any questions on training, please put them in the comments and I will support you with everything I have.

PS: This post was formatted with the help of @scroogers Markdown-Guide. Check it out and if you like it, resteem it and upvote it.