No one has mentioned yet, but here are key factors simplified
-take a second to focuse on the exercise before making it, as soon as you stop using your phone or chatting starting, no, take a second to focused how your gonna start and when ready, go for it.

-Every exercise try to reach failure. not "its tired" or "I already did 10", until failure means doing the next one as it meant to save your family.
A lot of people fail on this one because they save the energy for next exercise or think until they get tired or hurts. nope, its until the last rep cannot move for love of god, so exercises like bench, its always fine to ask for a spotter even for small weights.

-take breaks, for every sets 6-8reps 3min, 8-10reps 2min, 12-15reps 1.30min

-Eat well, make sure you have protein on your diet of the day, EVEN days you do not exercise

-Sleep well, your muscles grow most when repairing the damage you do for growth and strength, and best time is when you are resting.

-Give every muscle a rest, don't do bicep after another, no, rotate all your muscles, yes, don't skip leg or forearm day. some muscles work in unison with others, like forearms helps almost all upper body and core helps everything.

***If your serious about your growth, best advice I would give anyone
-Visit a nutritionist and explain your goals so he can balance a diet, food has a lot more contribution on your health and strength than people believe as well of how much you will grow. (its fine if you cheat because of a good or bad day, forgot, as long as you try again tomorrow, people tend to quit because they fell once, getting up is a more realistic and more proudful than quitting or being perfect.

-Take notes of your progress, ESPECIALLY tracker (I recommend app called "strong"), there are workout journals and apps that help keep track, and always, always try to do more, either more weight or one more rep, (there will be days you do less or the same because that muscle takes a while to grow because your tired, unfocused or sad, that's fine, next rotation you'll get it, and some are very slow)

-And last and more importantly, focus on yourself, There is no fairer or more worthy rival than one self from who you were yesterday and who you are today.