If it's important enough for you to spend your time finding and
connecting with new people online, it's important enough to get the
first impression right.

If you use any online social network tool, the single most important first impression you make is with the 3600 to 5000 pixels you get for your tiny picture.

In the social group I run, part of my job is to pick the featured members. As a result, I spend a lot of time looking at little pictures. Here's one person's take on the things you can do to avoid wrecking that first impression:

1. Have a professional or a dedicated amateur take your picture.
2. Use a white background, or at least a neutral one. No trees! No snowstorms!
3. The idea of having your significant other in the picture is a good one, at least in terms of maintaining peace in the presence of a jealous or nervous spouse. But the thing is, I'm not friending your girlfriend, I'm friending you. I'd vote for the picture to be solo.
4. If you are wearing a hat, you better have both a good reason and a good hat.
5. I totally understand that you are shy, modest and self-effacing. But sabotaging your photo is not a good way to communicate that. We just assume you're a dork.
6. Conceptual photos (your foot, a monkey wearing glasses) may give us insight into the real you, but perhaps you could save that insight for the second impression.
7. How beautiful you are is a distant second to how happy you are. In my experience, photos that communicate openness and enthusiasm are far more appealing than photos that make you look like a supermodel.
8. Cropping is so important. I should have put this one first. A well cropped photo sends a huge, subliminal message to other people. If you don't know how to do this, browse through the work of professionals and see how they do it. It matters.
9. Some people have started adding words or signs to their images. If your goal is to communicate that you are the website or you are the company, then this is very smart. If not, then remember the cocktail party rule: if you wouldn't wear it there, don't wear it here.
10. If, after reading this list, you don't like your picture, go change it. No reason not to.