I've had some horror stories and have learned a few rules:
1. If they have no pictures it's because they have a serious complex about their appearance, and possibly rightly.
2. If all of their pictures are neck up they are very, very large.
3. If all of their pictures are heavily posed then you will be disappointed when you meet them.
4. They are almost certainly talking to and meeting other people so even if you meet them and have a great time that doesn't mean you'll ever see them again.
5. No matter how old and experienced people get, they can still be incredibly immature and selfish in letting you know they aren't interested. If someone hasn't contacted you in over a week then drop it.
6. If you are a woman, use the functions to disallow people to contact you if they don't meet criteria important to you like, say age range. You WILL get LOADS of creepy weirdos sending you shitty messages.
7. If you are a man, actually think about what you are going to say in your message and if they are interested they will reply because your message will stand out amongst the sea of messages from creepy weirdos.
Also whilst typing this I got a text from a girl I'm meeting this weekend. I think I use these sites too much