How to overcome over consciousnesses and shyness?

im am a15 year old girl and i have a problem of over consciousness and shyness.whenever i go out with my friends or even at school , i become very over conscious. i become so conscious that i start walking with my hands glued to my legs... i don't move them at all!!!and not just that .. i'm also so shy that im not able to speak to people naturally. i always blurt out some thing wrong or stupid and i always make a fool out of my self. i'm not fat,not ugly,, in fact some people have also told me that im cute.. but i dont know how to be natural and normal!!!!!!!!!!!! PLZ HLP