Choose Rock.

Seriously, through my extensive experience playing there is about a 75% chance they will start with scissors.

Go test it out and youll find it's true.

And then I find that choosing scissors second usually wins--but that's less certain--and after that it's all in the air.

-I actually just looked up "how to win rock, paper, scissors" and it said always go scissors because most people choose rock. That's crap. Or maybe the trick is that you have to tell the person beforehand that you're really good and you always win--so then they if they were initially going to go rock they change to scissors. But honestly, I win this game way more than I should according to probability and it seems like everyone I play always go scissors first--like it's the clever choice.