My friend states he simply jumps at the top as hard as he can, but he is always off balance in the air.
When going off a jump, I flex my knees at the base, and extend my knees and then do a small, controlled jump at the lip, and then suck my knees up? I feel like my form is overall stable, but I am just not getting nearly as much air as my friends.
From your description it sounds like your form is right. Do you feel stable in the air? Then you're doing it right; get more approach speed to launch higher if that's what you want...
If your friend isn't stable then he's got some issues to work out!