I agree with a lot of the ladies on here so far. I'm sure I'll be repeating some things, but I'll just tell you what I would prefer when a guy PM's me.
Like Kotch said, if your main goal is to get me to look at your cock or inflate your ego, then stop now and don't even bother.
Don't say anything to me or ask me any questions that you wouldn't ask me in person.
"How big are your tits?" "What do you think of my cock?" "What's your favorite position?" "Wanna fuck?" If you wouldn't walk up to a woman in a public place and ask her these questions, then don't ask them of me either. The internet isn't an excuse to throw all manners out the window. I'm still just as much of a person in text as I am in real life and I expect to be treated that way.
If you are truly interested in me as a person, check out my profile before you PM me. I really hate when guys ask me where I'm from or how old I am. As soon as they ask me that, I automatically think they don't give a shitfuck about me or who I am as a person because they didn't bother taking the 3 seconds it takes to find that out.
One guy from this site that has now become a very dear friend of mine took an approach I like. We started chatting and flirting on the forums. He'd respond to my posts and I'd respond to his, etcetera. After a couple days of that, he PM'd me asking, "How do you feel about PM's?" Simple, polite, no pressure. I appreciated that.
Most women on this site appreciate cock, but we aren't cock-starved whores who want nothing more than to slob on your knob. Please don't treat us that way.
Sense of humor always helps.
Hm. I think that's it... for now, anyway.