The Internet is a massive library of information on your destination. Block out time to wade through sites, reading about culture, books, accommodation, and local transport. Consider the date the information was posted, and the credibility of the source. Don't get discouraged if you turn up nothing. Not everything is listed in search engines.
Some vaccinations require multiple visits to a travel clinic, so leave plenty of time.
Also visit your dentist. Women should get a gynecological exam. Inform your doctors that you are taking an extended trip, and take contact info, including e-mail and fax numbers, for all of them. Insurance Health insurance sometimes covers individuals outside of their home country, and sometimes does not. Regardless, insurance companies toll-free 800 numbers may not work where you're going, so call your insurer and get an alternative phone number.