I was totally anal for my first tour.

I had cycled for years (I've never even owned a driver's license), but no camping. Over the course of a couple weeks leading up to my first tour, I went out on several afternoon rides, each with a different load configuration. I thought, get used to the handling, get used to the load, and be prepared. In my mind, this all calculated into an intricately orchestrated grand strategy. Then I did a one night test outing. The plan was 100km out, camp, then 100km back. Simple. I skimped, not only on sleeping mats, but on a sleeping bag too. I thought, "hey, it's summer." I forgot, "oh, I live in Canada." So I slept on the ground with nothing but a thin tent and cycling shorts in about 12 degrees Celsius. After having injured my knee half way through the first day, I did the ride home one-legged and missed the ACTUAL tour I was planning because I couldn't even walk, much less ride.

Lessons
1) Don't plan for the expected weather, but the worst weather.
2) Don't ride on an injury. When the body fails, get off the bike.
3) You can only plan so much without experience. Be flexible.