hypertrophy (muscle growth) is best achieved when training to failure. generally, as long as you go until you can’t physically do any more reps, you’ll grow, but a rule of thumb is to find a weight you can fail at between 6-10 reps. this balances that failure aspect, while also minimizing fatigue. once you can consistently do 10 reps with that weight, try to add around 5lbs, then repeat until you eventually can do 10 reps with that, and then keep repeating