Do a little research. Before you write your profile, see what people your similar age and gender are saying about themselves.
Do remember that this is a dating site, not a job interview. Use your profile as a trailer, not the full movie.
Do actually date. Get out and meet in real life!
Don't sit idle. Aim for about ten new messages a day in order to get noticed by other users, and the site's algorithm.
Don't cut and paste. It's pretty easy to spot a generic "I send this to all the girls" message, and it won't do you any favours. Personalised messages stand out much more. and get a real dialogue going.
Don't mention how you promise you won't ever tell anyone you met online. The stigma attached to online dating is long gone. Be proud that you're being proactive in your search for love.