I used to be really shy... one of the things that really helped me was being a member of a scout troop. Once I left I then helped to run the troop, and being responsible for organising activities for, training, and disciplining 20 kids certainly helped.
Getting a saturday job behind he counter in a community pharmacy helped a lot too. As well as being perfect work experience for my uni course, and looking good on UCAS, it forced me to meet, talk to, and be friendly to people.
At my old school, it took me years to make any real friends. At Uni this hasnt been a problem at all.
Haven't overcome the fear of public speaking yet though. I can cope with smallish groups (e.g. when i was running the scout troop, etc) but not more than 40.