[snazz]

My personal recommendation for learning to give better presentations is to just do it. Start your own little tech convention and do as much public speaking as possible. You get the "bystander effect" at social events when someone has to say something to a crowd but nobody wants to do it, so step up and get some practice! People don't judge you for errors nearly as much as you think.

As for written communication, Markel's Technical Communication was used in my English class in college and I remember getting a lot out of following its directions. As you might expect, it's very well written. Of course, I had the advantage of classroom instruction, but I think it would be helpful even for self-study.