Agreed, I've used other sites, not OkCupid, but ended up with the same result. I keep it dead simple, write a couple of lines, and if they respond with a hint of interest, I just ask them out for something casual. It works really well. Approaches that failed...
1. Short messages like you said, 'hi, how are you?'. They basically get deleted instantly.
2. Long, thoughtful messages. I'd write a few paragraphs trying to make some jokes, and talk about what we have in common, and then ask a handful of questions about their interests. First problem, it's a lot of time on my end. Secondly, they need to invest a lot of time to respond. It's like those e-mails that you'll get to tomorrow, and then the day after, because you know they're going to be time consuming. Same thing, and eventually, they just say forget it, and never reply. Meanwhile, ask one fun question, and they can reply within a few seconds, and you're more liking to get a response.
3. Trying to keep a conversation rolling before asking them out. It goes downhill fast, and with every message, you risk them disappearing, or someone else grabbing their attention. I've lost count at the number of people I was talking with, everything sounded great after a handful of messages, then they fell off the face of the earth. Once again, ask them out after the first reply, and you don't have to worry about that happening.
In short, simple message, ask them out fast, and don't try too hard. Easy for you to write, easy for them to respond.