Ask yourself, "Would I say/do/ask this IRL?" 

Many an online faux pas can be avoided by considering the following: "If this woman was in front of me, would I act the same way?"

The application of this is endless. If a beautiful woman was right in front of you, would you ask her for a nude photo? Would you play it cocky and say, "I usually only date blondes, but I guess I can make an exception for you"? 

Please, be you. Don't exaggerate who you are, even about little things, like your interest in Charlie Kaufman films. Having seen Adaption once hardly makes you a "big fan." Keep it real.