Write something about yourself that shows you've read their profile, mention things you have in common, and show how you're genuinely interested in them.

In addition to the big, popular online dating services there are many niche dating services that attract loyal users.

This is probably the biggest complaint about online dating services.

If you're a woman, chances are the guy you're writing to is uncomfortable with a woman taking the initiative; forget him and move on!

Let me guess: you must be a woman, probably with an attractive photo.

Start with the free ones, and once you've gotten your feet wet you can try one of the paid services. On the other hand if their photo is poorly composed (or nonexistent), they don't write articulately or they are wishy-washy about what they want, keep looking.

Either you're super picky (in which case you won't have any better luck meeting people in a bar), or you're using the wrong dating services.

It sounds like the problem is not that you're getting contacted by too many people, but rather that so few of them are attractive to you.

If that's the case, simply ignore them and move on.

This would be a good time to read our Ten Things to Know About Writing Your Online Profile article.