I don't have any confidence in speaking, how can I solve this problem of mine?

I grew up in a family with a very overbearing father, he more or less sucked the self-confidence out of me. As an adult, I find I face problems because of this in speaking with people or talking at length about issues which I am even qualified to talk about. I always get the feeling that people will think less of me when I open my mouth - I don't even know how to talk with people.