How can I talk to her?

There is a girl at school/collage, and we are friends in a distant but close sort of way. We sometimes go for walks or go to the pictures together, but we are somehow distant. I would quite like to get closer to her in a friendship way. But when we are not specifically together, for example if we see each other in the hall, I can't seem to find the courage to say hello to her because I am very shy.

So if you have any suggestions on how I could get the courage to go up to her and say hello that would be good?