1. Give yourself a gear shakedown. After every trip, unpack and sort your stuff into two piles: on one side, essentials (such as first-aid supplies) and items you actually used; on the other, anything you didn't use. Take notes on what ends up in which pile. It will soon be clear what you need and what you don't.
2. Perform the same process of elimination with food. Most hikers come home with leftovers (read: dead weight). Aim for packing no more than two pounds of food per person per day, except on extremely difficult or cold-weather trips.
3. Invest in a scale and weigh all of your gear. (We like Feedback Sports' Alpine hanging scale; $65, feedbacksports.com.) It will help you shave ounces that add up to pounds and compare your current gear to new products when shopping around.