A common mistake newbie bodybuilders make is they train far too often, not even realizing they need to rest to grow – or at the very least, they underestimate how long it takes their muscles to recover.
It’s known that muscles in the steroid free trainee take around 72 hours to recover.
With this in mind it’s a good idea to ensure that after working a muscle, you don’t work the same muscle again within that time frame, or you will do nothing but set it’s recovery back and waste your time and effort.
If you find yourself regularly working muscles which are still sore and not completely recovered, then the program you are following is likely too much for you in volume or frequency, and you may need to consider switching it completely, lifting less volume (sets/reps), performing less exercises on a certain muscle, lifting for less days, etc.
The biggest mistake you can make is to think that by continuing to work with a program which is causing you recovery problems you will acclimatize to it and everything will eventually turn out well. Chances are this won’t happen and you’ll need to change things or you won’t make good progress at all.