In the Store: Go to a specialty shop and get fitted by an expert.
A good store should have a treadmill, or at least let you take a spin inside the building, to check fit and comfort.
If you know you overpronate (roll your feet inward), look for motion-control shoes, like the North Face and Merrell models in this section.
In the Field: Tighten laces on steep descents to get more stability and control, but otherwise loosen them up to allow for foot swell.
Use aftermarket insoles from Shock Doctor, New Balance, and Superfeet to increase support and cushion.
At Home: Clean mud-caked shoes with a soft-bristled brush and a mild soap.
Dry shoes in the sun, not the dryerbut not for too long.