I travelled for the first time this past summer. I was in Singapore, Indonesia, and India.
Don't drink from the tap.
Learn some local phrases (important things + funny stuff). There are lots of phrase books and translation dictionaries available for most major languages. Being able to greet someone in their native language goes a long way. The ladies love it!
Try all the new food you can! Just be careful and use common sense if sanitation looks to be a problem.
Be a good example of America! Most of the rest of the world hates the US just because, but if they meet a genuinely good and well-meaning person, it can change their perceptions.
Convertors and adapters come in very handy. Get a multi-national one so you'll be good no matter where you are.
I bought a skype account and a pre-paid cell when I was gone. Elsewhere in the world, it's more common for you to only pay for outgoing calls and texts, and incoming are free. You can have skype forward your calls to your pre-paid. You can also make your skype number local (your same area code) so your family can call you toll free.
You got your shots, so good job there. Like it's been said, carry some antibiotics and any other medications you think will come in handy (tums, immodium, etc).
I made a few copies of my passport and hid them in my luggage and on my person. I didn't want to end up without it at any point when I'd need to get the fawk out for some reason.