ArtVandelay, I think I've replied to you before and made a similar compliment on your allusion to Seinfeld, but I love that show. Anyway, everybody here seems to be giving advice on how to make improvements externally: smile more, confident body language, being interested in the people you're talking to, exc..
All good stuff no doubt, but changing inner beliefs can really make huge long term differences. I've never been very adept at visualizing so I maily use affirmations and conversational reframing. Conversational reframing is an awesome way to change beliefs, because you literally argue with it and test it in a variety of ways. If you do this daily I guarentee you will make some noticable improvements in your interactions with others, as well as internal confidence. I've been using a book called Mind Lines
. I highly recommend it.