Open the garage door and designate three specific areas on the driveway or the lawn. Removing the items completely will enable you to get to the bottom of the mess, and it will inspire you to finish the project today. Who wants all that stuff on their lawn?.
Area number one is for items you intend to keep. Area number two is for items you intend to give away or sell at a yard sale. Area number three is for garbage. Place an ad on Craigslist.com for your yard sale right now. The ad is free. While you're there, check to see if anyone is getting rid of any garage organizers. You might need one.
As everything in your garage is removed, be sure to sort it into one of the three areas. Be liberal with the pile of items to get rid of. If you haven't used the item in the past year (two years for seasonal items) then chances are, you won't be using it again.
Once everything is out of your garage, sweep the floor clean and analyze your garage storage options. Do you need to install a garage cabinet? Is your garage shelving in good repair? Are the shelves wide enough and are there enough shelves?
The items you have removed from the garage; are they clearly labeled? Boxes with no label should be inspected and properly labeled. An inexpensive way to do this would be with masking tape and a permanent marker. Many people simply write numbers on the boxes and keep a list of what's in each box by the number. This way, when it's time to pull out that old antique beveled mirror, you can consult your list and see that it's in box number 7.
You can add hooks on the ceiling of your garage to store bicycles, picture frames and other items. Stackable dairy crates are great for storing gardening equipment, hand tools and tool sets. Garage organizers can be set up in various places to help you keep track of your inventory of stuff.
Off-season clothing can be stored in stackable plastic boxes, with size and season labels.
Many garages have a corner set up for shop tools, whether they're for woodworking or automotive. Consider setting up a similar corner for gardening, sporting and storage of other items. Segregating the nature of storage items means that there's a place for everything.
Don't chicken out on the yard sale, your garage floor will stay clean if you get rid of the items you don't need. You can also drop them off at a thrift shop or shelter, too.