I have no idea. I have no problem with maintaining it once it's started, but I don't know how to make the first step.

"Hi, I saw your profile and you seem pretty interesting. What's up? :)"

Emoticon optional, depending on how easygoing you want to appear.

Read the person's profile. There should be plenty of a conversation starter there. For instance, if the person likes to read, and you know what she read, make a comment/question on that.

Do the same thing in relation to your own profile. You can evoke in your message something that is more detailed in your profile.

Whatever you say should be stated in a way that should evoke a response from the other person. Ask questions, explicit or implicit.

If their profile doesn't have anything that sparks conversation, you two probably wouldn't get along very well.