In the Store: Packs are like shoes: Get fitted by an expert.
Raid the store's shelves for the things you actually carry, and see how it all fitsand feels (add ballast with sandbags).
It's easier to compress than to expand: Choose a pack for your biggest hauls.
In the Field: Pack a symmetrical load, with heavy items in the middle, close to your back.
Make sure your hipbelt is actually on your hips (not below) and cinched tight enough that it won't slip down.
Stop to adjust shoulder straps and load lifters during the first hour of hiking.
At Home: Clean grungy packs with mild soap and warm water. Dry thoroughly before storing.
Remove grit from zippers with a vacuum.