Familiarize yourself with the art of Mask Acting.

Many actors out there are afraid of damaging their appearance or reputation if they act over the top in a role. However, once you put them behind a mask or inside an elaborate makeup piece, they become psychologically invisible to themselves and they are free to run loose. Consider Tim Roth in Planet of the Apes (2001). Do you think he'd EVER act as crazy as General Thade in any other role where he just looks like Tim Roth?

What you need to do is find something for you to hide behind to help you get into practice of being the non-shy you like most actors become when mask acting. I used to be a pretty shy guy myself until I got myself an interesting, unusual pair of sunglasses. I wore those wherever I went and I eventually became psychologically invisible to myself, so I was free of the usual anxieties that prevented me from keeping myself on the normally social reservation leash. I'm now just as open with myself and everyone I meet without the glasses just as much as I was WITH them. You need to find yourself a mask to hide behind.