Muscle-building is a process that involves trial and error and personal experiences to determine which techniques work for an individual. Here is one lesson I learned that was holding me back from achieving my personal muscle-building goals:
I was working out every body part every day. Yes, every day I would work out my upper body, lower body, abs, glutes, etc. Every single day.
This is a mistake I made when I first started working out (and actually for many years). I wasn't giving each body part adequate time to rest and recuperate from the strain I was putting on them.
Although I was able to put on some muscle with that technique in the beginning, I plateaued and couldn't seem to make gains for quite some time.
Then one day I made the decision to focus on just two or three body parts each day only and alternate between upper and lower body parts. So, for example, Mondays I might only focus on my chest and back, Tuesdays on my biceps and shoulders, Wednesdays on my legs, etc.
Once I started doing this focusing technique, I started putting on more muscle.
This is just a simple technique anyone can do and likely start to see bigger gains. Of course, I can't guarantee it will work for you.. this is just from my personal experience.