I met my wife through adultfriendfinders.com. But I did a good deal of work and effort to get a good ad there. I regularly got responses back from the women I messaged, and met several people for coffee before I met and fell for my wife.
For internet dating sites, for men, I have a few REALLY GOOD tips.
1) sign up for a woman's account.
In other words, sign up for a free ad, and post that you are a woman, red-hair, athletic build, non-smoker, looking to meet some new people and have some fun. Don't post a picture. Then sit back and watch the messages *FLOOD* in. If you want them to come in even faster, mention that you have big boobs. Read the messages that you get. They will be a fantastic guide on exactly what NOT to say to get someone to respond to you. 90% of them will all say the same thing, with various measurements given between 9 and 12 inches. Most of those will end with requests for your phone # and address. Most all of the others will be something insipid or stupid that will make you roll your eyes and mutter "loser" under your breath.
2) Do *NOT* spam the same message to all of the women who match your search.
Many of the women out there have more than one account on the same site, and will catch you if you send them the same message to different accounts. There are a LOT of "spammers" out there who get disqualified immediately for that.
3) When you do find someone that sounds like you'd be interested in talking to them, *read*their*ad* and respond to what it is that they said about themselves.
She says she likes cycling? Ask her what it is that she likes best about it... etc.
Also, a great idea for an attention grabber, or ice-breaker is to sympathize with the fact that she is being deluged with stupid messages.
Basically, understand that your message will be one of hundreds that will be flooding into her mailbox. You have to stand out from that crowd, and you have to do it by being interesting, down to earth, realistic, and interested in her. Once you can do that, then you'll start getting replies back to your messages. And once they start talking to you, then you can pick and choose which of them you want to spend time with.
Just pay attention. That's really the important part.