I've seen a few other people address this on other threads, but I'd like to make and emphasize a few points about talking to girls online that I think will be helpful. Some of it's just common sense, but all is stuff I've dealt with myself and seen personal improvement from addressing. This is far from complete, so if anyone has any other tips to add, please do so.
1) Keep it simple. You don't have body language to read or other cues to pick up on, so calibrating is far more difficult. Girls often participate in conversations just to appease you - without paying attention to what you're saying - and online you have no way of knowing when she's lost interest. Keeping it simple keeps you out of danger. If you're having conversations where "lol", "cool", or "k" make up the entirety of a response, it may be time to reassess the situation.
2) Rhody mentioned this recently on another thread, but it's important and needs restating: use proper grammar, spelling, and punctuation. These things are vital to online game. Even though the conversation is non-verbal, we process things we read pretty similarly to how we process the things we hear. If you don't know basic rules about punctuation - which some people may not - at least be sure your sentence makes sense. Regardless of who I'm talking to - unless it's a good friend who I'm totally just shooting the shit with - I never send anything that I haven't reread first. Imagine how it sounds in your mind, and if it doesn't flow easily and make sense, make it so. If you feel like a pause would be good at a certain point, put a comma there. If a certain word sounds bad coming after another word, move it. Make it easy to read and understand what you're typing.
3) Be nice! She can't see you, so you don't have a handsome smile and relaxed body language to go along with your negs and disqualifiers. You want them to be effective, but not taken too seriously. It's easy enough to throw a neg in-field and then carry on with your story, but online, everything you say stares her in the face for another few minutes until it gets pushed off the screen. I'm not saying don't do it, but be mindful of these things when you do. If I'm negging online, I usually start the sentence with a "haha" or end with a smiley face.
4) Remember to be the exception! It's easy to make little lists when talking about what you're looking for, your interests, etc. Every AFC out there says "I'm looking for someone I can relate to," "I like people who make me laugh," "I like honesty and communication without bullshit games." Who the hell doesn't want those things? You can also sit there and say "I like to ski, fly planes, play laser tag, skydive, volunteer to entertain cancer-stricken children, learn new things, etc," but again, you're just listing interests, and no matter how interesting they are, they're just words. They don't convey personality, feeling, or excitement in any way. A faked "Oh, you fly planes?!" is the most you'll get out of her. The solution? Tell stories that CONVEY all of these things. Don't tell her you're a funny guy with a good sense of humor: SHOW IT TO HER. Don't list your interests, tell her ABOUT them, how you got into them, where you do them, how you feel when you're doing them, etc. That's the shit that attraction is made of.
5) Don't have bullshit meaningless conversations. A lot of people keep their AIM/MSN/Google open all the time and talk to whoever happens to be online. Ever had a "hey, sup? nmu? nm. cool" conversation? They're a waste of time and nobody really enjoys having them: it just DLVs you by showing that you don't have something better to do than idle at your computer waiting for people to talk to. Plato once said "Wise men speak because they have something to say; Fools, because they have to say something."
Be the wise man.
