Do not sit on "mass", do not eat everything, eat right and gain pure muscle mass.
Do not overdo it with the volume of load (the number of approaches) so as not to overtrain.
Follow your exercise technique so you don't get injured.
There are a billion more nuances, but this is perhaps the main thing.
Before starting training, I would advise you to read a lot of information, both in video format (there are many professional bodybuilders on YouTube with their own channels in which they set out pretty smart things), and in text (there are many articles on how and what to do). Although in the process of training you shouldn't stop learning new things, you need to constantly read and learn something.
From myself, I can say this: -With the help of a calculator of your body, find out how much you need calories, proteins, carbohydrates per day -Eat right (eggs, chicken breast, buckwheat, rice, oatmeal, vegetables, etc.) -Make a correct and convenient training program (Practice ~ 1 an hour, a break of 1-2 minutes between each approach, do everything slowly and clearly, feel the muscles)
It's nice that the author of the question considered it delicate and became anonymous)))
Find a normal coach and take personal training, and not scour the Internet looking for advice from random people.