Tips on how to get over this?

I am an extremely shy person. Most of my friends are very bubbly and outgoing and I love it because that means less talking on my end (I'm also a quiet person). This does pose a problem when guys come up to me and talk to me, even if it's on a platonic level (like if they come up to meet me). If I find a guy attractive and he goes out of his way to talk to me I can't even look at him, I get shaky and I'm even a bit afraid to talk too much (for fear that he might not like what I have to say). Any suggestions on how can overcome this?