Sort all items into three piles: keep, donate or sell, and toss. Lay them on dedicated tarps or mark off areas of your driveway with chalk and place them there. What should get the boot: outgrown toys, items that are broken beyond repair, expired household chemicals (which may need special disposal), and anything you haven't used in two years or more. If you have a hard time letting go of things that have sentimental value, snap pictures as keepsakes.
Sort the keepers into broad categories (for example, sports equipment, hand tools), and place them in well-marked cardboard boxes or, better yet, stackable clear-plastic bins you can use later. Put the keepers back in the garage for now.
As soon as possible, donate giveaways and schedule a yard sale to get rid of castoffs. If you've got too much trash for your hauler to take, use a service such as Bagster (thebagster.com
); simply buy the bag at a home store, pack it, and contact the company to schedule pickup and disposal (fees vary).