Strength, height, and athleticism are great assets, and coaches love those types of intangibles. That being said, coaches look for the following abilities more than anything else: clean route-running, good hands, and receptiveness ("coachable" players). Height and size don't matter if you run sloppy routes or drop passes thrown your way. You'll find a spot on the team no matter what if you prove yourself as the most technically-polished receiver out there. Also, make sure you talk to the coaches and prove to them that you're a determined player. Ask questions, heed their advice, and really study the game. Don't simply go through the motions -- make yourself stand out, and let the coaches know you're determined to make the team and contribute to it's success.