Whenever you are around him, talk to him and be flirty, but not too much- keep it casual and easy going. Hopefully he will get the drift and feel more comfortable in asking you out once he suspects you are interested in him. Dropping hints that you like him might do the trick, however some guys may not even realize you are dropping hints even if they like you; in fact, if they like you, they may be feeling even more scared of possible rejection.