The way that we deal with our peers is partly based on how we view ourselves. If we see ourselves as weak and easily influenced, then our peers will see that in us too. If we feel strong and individual inside, our peers respect our viewpoint more.
Low self-esteem makes us sitting targets for those peers who like people to do things their way; by building self-confidence we can more easily stand up to people who want to coerce us to their way of thinking.
There are lots and lots of books, CDs, online courses and tutorials on how to build self-confidence and believe in ourselves. Not all of them are relevant, so select the ones that you think apply to you and your situation and use them in your own time. You will be surprised how this can help.
If you feel really low and can't even find the inclination to get some self-help material, you may need to see your GP. Low self-esteem can sometimes be an indicator of other things in your life that need attending to.