Just be yourself, hopefully you have a witty personality. I'm personally very witty (naturally). I didn't know that until a 10 commented me one day and said "Lol I love reading your statuses! They're so funny and witty!"
I have a gf so I wasn't doing it on purpose to get chicks that's why I never noticed.
I guess you could just sound fun and make it seem like you have a life. Don't post stuff like "Bored" and don't complain. Don't post super long statuses either. That's just my opinion but that's probably cause I have a short attention span haha.
Btw, I could easily give you examples that JUST WORK, but what's the point in getting online attention if you're not like that in person? I've always believed you should act the same online as you do in person.
