Hold his hand, hug him, kiss him, put your arms around him, you could put your hand on his knee and really its just about snuggling and maybe even footsies (if you like that)
when sitting next to him make sure you are always touching wheather it is his leg, he hand or anything
lean up and kiss him
surprise him with a squeeze to the crotch ;)
whisper something dirty in his ear like " I want you so bad"
"accidentally" trip into his arms <3 (works every time;)