I'm shy; it's how I grew up having two older sisters and going to private schools.
I came across some blog a while back talking about forcing eye contact; since (for me personally) can be something I seriously struggle at; the practice / tip (maybe lifehacker?) was to just make eye contact with people while walking down the street, until they notice, if they do just smile, and go on to the next; and the more and more you make contact the better off you'll be while in conversation; it's still difficult but it's helping for me.
Today was visitation day on campus at uni; parents and highschool kids everywhere, I work for our campus recreation but I was taking pictures but had a family stand in front of me talking, so I butt in and answered all the questions they had. Definitely not easy for me, I worked up a near sweat just freaking out on the inside but kept as cool as possible.
It's hard, it really is.. you just have to do it more and more, otherwise you'll stay the same; it's just super hard to break out of that shell I've made myself throughout middle and highschool.