Most Helpful Guy
You don't. All you can do is increasing your chances. If you're pretty sure he likes you, then just be around, be nice to him, make him think about you. If the have the guts to ask you out he will. If he doesn't, then ask him out yourself, you won't wanna regret later for something you could've done.
Most Helpful Girl
Make more eye contact maybe smile a but.. it might work or maybe just ask him out