If you've got more serious problems, like a longstanding eating disorder or body dysmorphia, the ideas below aren't going to do much compared to getting more dedicated, intensive support. If you're mildly or moderately unsure about how you look then the ideas here might help you feel better. A topic like this needs a couple of disclaimers: This longer article gives many suggestions about how you can become more confident about how you look. Most of us have been insecure about our attractiveness at one time or another.
Of course it's hardly just socially awkward types who have these kinds of doubts. One area they can be unsure about is their appearance. People who aren't happy with their social situation usually have insecurities.