You might try to add nonverbal cues such as leaning forward or a slight hand gesture to draw attention to yourself when you have something to say, before the current conversational chunk is done. This will help warn others that you would like to speak. Watch other people in the conversation to see if you can identify other cues, since people probably are more receptive to cues that they use themselves.
Edit - many apologies to anyone that feels that this discussion was a waste of time.
I just ran across an article (http://techno-anthropology.blogspot.com/2011/04/rough-guide-to-social-skills-for.html) on Hacker News that gives the barest minimum of a guide for social interaction. Unfortunately this isn't the high-quality advice you need to really handle social situations, though it will help with a few of the worst problems.
A few other rules that will help:
On the physical side:
This is a long list, and it isn't even close to complete.
I'm linking to http://lesswrong.com/lw/372/defecting_by_accident_a_flaw_common_to_analytical/ at the suggestion of David Gerard. It has a lot of deeper discussion into why this is worth knowing.