Obviously the pic is most important. Good candid shot.

Don't be afraid to write a lot about your life. Don't go on and on about yourself though, as in your tastes and dreams and all that shit. Stick to lifestyle. Stuff you do, stuff you're going to do soon, stuff you want to do eventually. Think of yourself as a salesman and your life is the product. If a prospective date is going to buy in, it's because of a desire to participate in that life. You don't want to leave a question/doubt about whether you're worth a couple hours out of a weekend.

Don't waste too much time. Express a direct interest in meeting. Just be considerate about comfort and safety in your invitation. Demonstrate that you're a thoughtful human being. But at the same time, don't let yourself get dragged along forever.

When messaging, don't get too serious off the bat. You'll sound like a reporter doing an interview. Play into humor you see on the recipient's profile. Keep the message short, like some joke you'd crack in passing. Everyone wants to be left smiling.