Make sure the travel agent knows what you like and don't like. Talk about this upfront. No need for her to book you on a night club crawl when you hate the night life. Be selfish with your money. Read up on tipping and the tipping culture. Some countries don't really have a custom of tipping so anything you give is a surprise and delight.
Cover up your US passport. Put it inside a discreet outer cover. Believe it or not, there are a lot of places around the world who simply don't care much for Americans. Best to be safe than sorry.
Be sure you understand the macro politics of the country you will be visiting. If in doubt don't share your ideas a lot if at all. For instance, a casual disparaging remark about the government of Thailand or Cuba can get you put in prison for years. This is a true statement so don't test it.
Finally, keep a journal, especially if you don't expect to return to that country again. You will be amazed at how quickly you will forget the small things that made the country so special.
Now keep dreaming or get going. In either case ENJOY!!!!