Don’t pick a creepy username. “Clever is better than boring, but boring is better than gross.” Most potential dates won’t find sexually suggestive names as funny as you do.
Use current photos. The whole point is to date someone “who is attracted to you right now,” not the you of “six years, 25 pounds, and two high-stress jobs ago.”
Be honest, but not overly so. “A bit of humorous honesty is a plus”—you like Twilight, you “once ate dog food as a kid”—but leave out fetishes or rants about your ex.
Date in your age range. If you list a range significantly younger or older than yours, people will think there’s something wrong with you.
Write coherently. “Use proper punctuation and make sure most of the words are spelled correctly.” Unless, of course, you want to date someone who’s a little slow.