How to grow the biggest bubble butt?

So my booty is a tad small, (as well as everything else, I am a tiny twink) and this year I've decided to make my body look more sexy for men. Going to get a gym membership and work on it. Definitely want to have a great ass by the end of it though and need help on how to healthily achieve that. Do any of you guys have any tips, routines or exact things to do? Never been to a gym before and have no ideal what to do and really anxious about people seeing me.