Preparation is key. I take the time to log my progress as a project moves forward: commit notes for the code and diary-like notes in my To Do list. Just two places, all electronic and off-site, no post-it notes or written folders or binders.
If I have a meeting I can prepare for, then I always take the time to prepare any relevant talking points on my laptop: the crux of the situation, long term goal, current hurdles, and possible solutions. If someone walks into my office and asks for a report, I have my latest notes at the ready. If someone meets me in the hallway, I've been writing my notes for so long, I can generally recall broadstroke information from memory. If I have my notes in order, then knowing what to communicate about is a cinch, and that makes actually speaking about it easier by extension.
If it is a matter of simply not being used to speaking in front of a group of people, nothing gets over that like practice, practice, practice.