Don't laugh at his jokes in an exaggerated manner. It's patronizing.
Ask him about himself and take some (but not all) responsibility for keeping the conversation going.
Don't sleep with him. (I don't mean to imply anything about you. Just saying it's not effective for keeping him around.)
Offer to pay your half but let him pay if he wants to. (Next one's on you.)
Don't show him any parlor tricks like drinking milk through a straw that's up your nose. (You've got to save *something* for the 2nd date!) Also hold off on telling him stuff like how much you like chewing tobacco, for example.