How to get him
Let me be honest here. If what you want is a long-term steady relationship... with THIS guy in particular... well then, you'd better be a cat person (and by cat person, I mean, furry, with a tail and pointy ears). But if you just want a little fling, well, then all you really need to secure his attention is a Wonder Bra.

Competition
If you're willing to overlook chronic unfaithfullness, then your only REAL competition is Puar.

He likes you if...
The thing about Yamcha is not getting him to like you, that's practically guaranteed if you have breasts. The real trick is HOLDING his attention.