My thoughts on online dating, in general, is that it's a lot like regular dating, and slightly better than a singles bar. (Though I went into detail on it here - link I say go for it if you want, but not specifically just to get a date on Valentine's Day. That would be wrong.
Five things you should know?
Number one: Actually fill out a lengthy profile. I'm serious, talk and talk alot. There are a few reasons for this. One, is because if your profile just consists of cute, pretty or sexy pictures of you - or if it just consists of pictures of you - and nothing else, then the only possible messages you're going to get are from guys messaging you on your looks alone. It's simple logic but true. So fill it out, or you have no right to complain if a guy turns out to just want sex. When you do fill it out, try to think of as much to say as possible so that people know who you are, but say just enough, so you can bury things in the mix, to see if he was paying attention.
Number two: Never respond to a hot guy who's initial message is (or similar to) just "Hey" and nothing else. Any guy who does that is usually stupid and / or shallow, with the intent of just getting sex. If the guy read your profile, and had nothing to say about it, or nothing interesting to say about himself, then he's either not interested in you, or he's got nothing to say. Either way, the relationship will come down to just sex. That's not usually ideal.
Number Three: Not giving information that is too personal, or makes you easy to track down. I mean, there are many people who portray the internet as if all men are rapists who will lie about everything, just to meet you and stuff you into a van, but that's stupid. This is just the fallacy that contributes to the stigma on internet dating. Still, it's best you remain at least a little anonymous, in case things don't work out. After all, look at all the stalkers on Facebook, right?
Number Four: Common sense is your best tool. Basically just think about what they say. A good profile can say a lot about someone, even if they're lying. If you exercise common sense you should see the holes in their story. But the more you talk to someone the more you can get to know them, and a good profile aides in getting to know someone. It's the foot in the door. Just figure out who they are as they talk. Kinda like real life.
Number Five: Don't let one, or a couple bad experiences get you down. Internet dating is just like regular dating. There are good people and bad people. Some you'll want to talk to, and some you should steer clear. Use common sense, along with the other three pieces of advice, and it should help you weed out some of the less desirable people, but remember, just because the last guy sucked, doesn't mean should write off everyone else. The internet is Soylent Green. It's people.
Good luck out there.