Most Helpful Guy
You jump his bones.
No I'm just kidding. Hold his hand sometimes, sit closer to him when you're sitting together, don't be afraid of leg-to-leg contact and things like that, just basically reduce the amount of personal space you typically keep between each other.
Definitely flirt more, not less, but otherwise mostly just act the same. Tell him you think he's cute sometimes, and then just try to find stuff to do together. Like dates.
Ask him out.