For me, the planning for a long distance hike goes in several stages:
1. First is the germ of the idea.
2. Next, I decide "yup, this is what I'm going to do."
3. Then I start gathering general information, like how long it will take, what types of unique gear I might need this trip, where the trail begins and ends, the general route, and so on.
4. Next, more specific considerations: The ideal "weather window" to avoid deep snow early and late in hiking season. Options to get to the trail-head and back. Ordering new gear. Making arrangements to get my affairs in order before departure. Arranging for permits.
5. Finally, planning specifics. And that's what I've been doing all day today. My most valuable resource is "Yogi's PCT Handbook." A veteran long distance hiker, Yogi tells exactly what a thru-hiker wants to know. Distances between resupply points, best places to take a day off (known as "zero days,") the most important places to mail food, regulations for bear canisters and fire permits, where and if ice axes are necessary.
So today, with Yogi's book and Craig's PCT Planner I have been getting a good idea of where I will be mailing food packages, (for me about nine places along the trail, elsewhere I'll buy-as-I-go) where I might take days off, where I'll mail guidebooks and other printed information, and where I'll send special gear (ice axe, rain pants and mitten shells, bear canister, etc.)
Good planning is helpful, but even more helpful is being flexible and maintaining a good attitude. I'm sure I'll modify my plan when the real world situation doesn't match the theory.
I plan to start my hike on the Mexican border near Campo, CA, likely on April 22, and with a little luck finish in late September in Manning Park, BC.
I love the feeling of an imminent "grand adventure!"