Not that I'm an expert - but I'd go with: Don't do/say anything you wouldn't respond well to if you were in their shoes.
Gay guys have a habit of starting conversations online with the words: horny, sexy, top/bottom, masculine, hot and "hey - how are you". I avoid those words. Just avoid sex as a conversation starter.
Personally, I always find it nice to know someone's taken the time to read my profile. I mean if you're looking to start meaningful conversations - why not start by finding what means something to the person you're interested it.