Write your profile. Be sure to be honest in your description of yourself and what it is you are looking for. There is nothing worse than someone who lies about their physical description. I have heard horror stories from people who say they expected to meet a certain person, and the person who they met was completely different. It is also right to be honest with yourself and the people you may end up dating. If you want someone who is outgoing, fun-loving, and intelligent, that is what you should put on the profile.
Put a photo of yourself on your profile. You should use a photo that was taken recently. The worst thing you can do is misrepresent yourself. Do not submit a photo of yourself that was taken ten years ago. You are who you are. Be proud of yourself and own it!
Be descriptive. Explain yourself in detail. Do not use vague statements like "I like tacos". You need to be more descriptive. Instead of saying that, you might say " I really enjoy Mexican food. Some of my favorites include chicken tacos, chile relleno, beef tostadas".
Have fun. More than anything else, have fun. Online dating is meant to allow you to meet new people. It can allow you to meet someone you never would have met otherwise. Just enjoy yourself!