How can I develop my communication skills?

I have a lot of trouble getting what's in my head out when I am speaking. It scares me and I desperately want to fix it somehow, no matter how long it takes. I am 15 and my mum is always saying that it's just because of my age and that it will improve as i get older, but I don't think that. My Dad has a lot of trouble communicating and suffers from depression and I don't want to follow him there. I am not a very talkative person in the first place...I'm more of a listener...but I feel like it's just getting worse. I read heaps of books (apparently that's supposed to help) and I think it does a little bit, but not much. In conerversation I would be talking and then suddenly loose words for what I'm trying to say! Like a mind blank, sort of thing. I just sort of trail of into this silence.....................Sometimes I hope people will get the general drift of what I'm trying to say, but I know they notice it. I really want to know how to be able communicate verbaly in a fluent way. Any suggestions for what i can do would be much appreciated