1. The more sets you do, the stronger you get
Wrong, more sets do not mean more (muscle) strength. When you want to get stronger, you have to train with a properly programmed volume to get a good response from your muscles. When you want to get stronger, you train at the edge of your ability. You make sets with 80-100% of your 1RM (1 repetition max). As soon as you do too many sets, it demands so much from your body that you cannot recover. If you cannot recover sufficiently, you will not be able to perform optimally during your next workout. This is different for each person and is also determined by the level and experience of the strength athlete.
2. If you want to reduce belly fat, you should do more abdominal exercises
Not true! You can't burn fat locally. So you can keep doing crunches and sit ups, but that won't melt the fat off your belly. To see your abs, your fat percentage has to come down, strength training will certainly help with that, but a healthy and balanced diet is an absolute must when you want to lose weight in a healthy way. So keep working out at the gym and get a tight belly by combining it with a proper diet!
3. You should work out every day
Nope, wrong again. Some people insist on going to the gym every day because they think you should ''train'' your muscles as often as possible in order to get the best results. The truth is that resting the muscle groups you trained is the most important thing. For optimal muscle growth, your muscles need 48 hours of rest. So you can do a full body schedule 3 times a week, or do a split schedule 6 times a week. As long as you give the muscle group in question enough rest, you can go to the gym as often as you want. Still consider sleep, stress and nutrition. These factors must be optimal to get the most out of your workout.
4. To gain broad muscles, you should only pull weights every workout (8-12 reps for more muscle mass)
Building muscle mass is not as simple as ''just pumping''. It goes beyond that. To build muscle mass, 8-12 reps is a good guideline because it's proven that this is where you focus most on hypertrophy (muscle mass increases). But if you use the same weights and do the same number of reps every week, your body will get used to it and be less likely to adapt. So write down carefully what you did at your last workout and make sure you have a progressive workload. Maximal strength can also help; you get different (and therefore more) stimuli with maximal strength because you can lift more weight again.
5.You need to do something different every workout to keep surprising your muscles if you want them to keep growing
Once again, bullshit! You only see results when you train consistently for months or even years. Not if you do something different every workout or pick up a different training schedule after 2 weeks. For the development of muscle strength and endurance, consistency is the most important factor. Also, doing 30 different exercises makes little sense. Even though many different exercises will give you muscle pain over and over again, muscle pain is not an indicator of a good workout. Muscles grow by doing more and more. So stick to the classics, build up slowly and add more and more weight. The top exercises to do this are standard in any strength program: Squats, Bench Presses, Deadlifts and Pull ups!