Read and Talk
Read everything you can find, in print and out, about the route you plan to take. Many of the older trails and established routes have guidebooks, as well as narratives written by people who have done them. Read them all. Guidebooks and narratives are very personal; one person may have hated the walk, while someone else loved it; one person may complain about animals, blisters, and weather, while someone else was unbothered, or had interesting ways of dealing with these things. Read as much as you can, and find out what you're in for. When I hiked the Appalachian Trail, I ran into other hikers at the beginning of the trek who had seen a television special about the trip and had not done any further research; they said the show made it look "fun." They had no idea how difficult the trek was, how steep the mountains were, or that at times, they would spend a whole week walking in rain before reaching any town where they could rest and resupply. These hikers dropped out early, within days of starting the walk. Hikers who had studied the trail were warned about these and other hardships, and knew that the long-term benefits of the hike were worth it. They also knew how to deal with the difficulties of the walk. These hikers kept going.
In addition, talk to anyone you can find who has done the trip. Ask for advice in planning; ask what they would have done differently, what was a "must-have" on the trip, and what they didn't need at all. For established hiking trails, you can often find experienced people by posting a notice at your local gear shop saying that you are planning to do the trail and want to chat with someone who has done it. Hikers tend to be a friendly bunch, and most will be glad to help you. If the Trail is overseen by an organization, call the headquarters and see if they have any advice; many of these organizations will send out a packet of information, for free.
The Internet can be a great way to find trail information. Recently, while planning a hike on Vermont's 270-mile Long Trail, I found maps, hiker reports, advice, guidebooks, and other information on the net.
