(1) Be ridiculously attractive, hilarious, or drunk--ideally, like Hannah Hart, all three.
(2) Don't eat for a full day before you record to ensure a slender look and absence of food in your teeth.
(3) Look at your phone from time to time and say, "Isn't that nice, Tyler Oakley* has texted me again." *Gamers should use PewDiePie.
Or just be yourself and have fun!