it'll just balance out on its own if there hasnt been an injury on it, what i did when i first started/ kinda still do is whenever doing dumbells i always do my left side first and if i only got like 7 reps in thats how many i do with my right arm even if i knew i could do more, i always made sure my form was correct when doing barbell workouts aswell, always made sure both sides whent up at the same time.. then again i'm kinda ocd when it comes to that kinda stuff
dont know why but the thought of one side being bigger than the other has always bugged the bejeepers outta me, both sides are the same strength now but i swear ones bigger than the other, must be mental or something cause everyone else says they cant notice