Its really hard to tell, and depends a lot on what type of a guy he is, but he will most likely do one of the following:
-Sneak glances at you if you are alone with him
-Make mocking kissy faces at you
-Allow his and your head to get close together, even if its not a prime kissing position.
-Stare into your eyes, or maybe at your lips
-He will say so
-Or he might surprise you and just go for it when the moment is right.