Get out more. Shy people tend to have small circles of friends and don't normally strike up conversations with strangers. Start going out to more places and meeting new people. Just making a few more friends can help get you one step closer to a girlfriend. Try socializing with a few co-workers you don't normally talk to outside of work, go out with some people you know from the gym or ask your current group of friends to invite more people along. Try to have a few girls in the mix. The more girls you interact with on a social level, the more comfortable you'll become around them.
Move slowly. Don't feel like you have to be the most charming guy in the room right away. Start with a simple smile and hello to a girl you could be interested in. Knowing that you're not planning to strike up a conversation will make you less nervous.
Start small. When you meet a new girl that you might like to spend more time with, don't feel like you need to ask her out for a date right away. Start with something more friendly that shares something you have in common, such as studying for a class or hanging out in a book store or coffee shop. Keeping it casual will alleviate your fear of rejection and help the girl get to know the real you.
Act confident. Even if you don't have all the confidence in the world, just acting confident can go a long way. Be assertive, but not aggressive and make eye contact to engage her. Be careful not to seem overconfident. Girls are attracted to confident men who also aren't full of themselves.
Ask questions. If you're genuinely interested in what the girl is saying, she'll pick up on it. Be an active listener. This means following up on what she says, making eye contact and not changing the subject after she speaks. These are all traits of what many women want in a boyfriend.
Keep your feelings casual until your interaction turns into a real relationship. This means not assuming you're going to date or not going to date every woman you meet. Talk to the women you meet as you would a friend, to take the pressure off, and don't think it's the end of the world if it doesn't go anywhere. If you do get rejected, try not to take it personally. Eventually, you will hit it off with someone, and if you be yourself, it may well turn into a meaningful relationship.