1. yes firm hand shake (but not too firm, and not too prolonged), smile, speak clearly and at a good volume. you want to sound confident, and you should be confident. look them in the eyes, but don't be afraid to look away from time to time when developing an answer, etc. you don't want to STARE at them. also, don't be afraid to use your hands from time to time when explaining something. don't feel like you need to keep your hands perfectly still or anything. don't overdo anything essentially.
2. yes send thank you notes. like pink/\floyd said, it may not help, but it can never hurt unless you spell their name incorrectly, or make yourself look like a fool in the note. if you had something that really stuck out in your interview, like they were really interested in X on your application, and you can find a way to tie it into your thank you note, do that so it reminds them of who you are (they see a ton of people every week). for example, at lunch, one of the interviewers with whom i did not even interview, started talking about state birds and what not, and i brought up a specific breed of birds that he had never heard of. i started talking about how fascinating and awesome they are, etc. he really liked that he goes "whatever you got on your MCAT, add 2 points". we really hit it off. i plan on sending him a thank you note just because we connected over lunch and i'll mention the bird species in a non-chalant way. that kind of stuff gets you remembered. don't try too hard in the thank you notes, but be sincere, and HAND WRITE THEM.
side notes:
unbutton your suit jacket when you sit down.
i would try not to take a seat until they ask you to, or until they sit down, unless it's super awkward, then just sit. but don't just march in and plop down right away.
if you have to go to their office, obviously knock (not too loudly) and wait to come in until they invite you in or they start talking to you
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