Your "vibe"

Your vibe consists of the way you come at people. It includes, but is not limited to your attitude, tone of voice, and the body language you give off. The way you talk to people is a huge deal for many men. Being overly rude or obnoxious is a turn-off. Standing in a guarded position may make you look unapproachable, even if you are not intending to look this way. A friend of mine tried this out when we went to a bar a while back. She was chronically single, and wouldn't even be approached when we were out. The crazy thing is, she is beautiful. She tried "letting loose" and it worked. That night she gave out her number to three different men. As it turns out, one of them is still seeing her.
Put yourself out there

Don't fear rejection
Many women are afraid to be rejected. The fear is natural, but can also be incredibly hindering. If you have noticed this as one of your issues, you need to consider the flip side of the coin. Dating the first guy you meet long term does not mean that he is the one that is "right for you." The relationship may last six months or many years, and then you are back in the same position again. There will be many rejections that you will have to deal with, including in love. Remembering that it will not define you should help you be able to get out and try. Sometimes there are sub-conscience reasons why you are still single. Think about your past experiences and what you could do better in the present. Consider this more about strengthening your social skills and gaining more friends, rather than just a simple quest for love.