[mockturtle]

my thoughts:

-work hard to isolate the problem, problems, or biggest problem. you say you have a hard time explaining things/expressing your views on the subject at hand. since i'm assuming you actually know what you're talking about (or you would have called your post "Learning to bs") the problem is either quickly organizing your thoughts and preparing them for delivery or actually speaking.

-if the former
i'd suggest spending time journalling, or writing in general (articles, blogs, etc). it's probably important you don't just write "i did this today, and this, and this" but focus on what you're having trouble doing, which is explaining a complex story and idea. furthermore, make these "stream of consciousness" since you mention this problem does not cross over to forums, since you have time to edit, conceptualize, etc. you want to be getting words on the screen or paper as fast as you can.

-if the latter
one of the best things to do is practice, starting with areas in which you are most comfortable. people here have given you many suggestions along the line of acquiring practice socializing and speaking. do not be so quick to put off "nerves". many of us can have anxious and nervous reactions (and probably do to some degree) that manifest themselves in a variety of ways of which the only thing in common is lack of success. there's no shame in it, it's no big deal. there are a zillion different people who can help you in all sorts of ways depending on the angle you're coming from, so i wouldnt know what to suggest (posts here are good examples, though). the key, though (in my opinion), is to make sure you're relaxed. signs you are not relaxed are tensing muscles, flexing your posture forward, speaking too fast, and holding your breath. keep aware of these things and if you see them happening, try to consciously work on it. maybe that will help you :-)