I want a really lean and ripped body, and not buff?

what are the things I should avoid (or the things i should do) in order to not end up getting buffed. i just started training at my gym with a trainer but i am kinda apprehensive about his nutritional and workout guidelines, as he himself is ridiculously buff. in other words HE IS HUGE!!!! i have a small-medium frame (not sure which one exactly), so yeah having those huge arms and chest would really make me look like someone from a different planet or something. i want to me as lean as i can be, but pure muscle nonetheless. thank you for your time