Most garage spaces contain a lot of unused space along the top edges of the walls. This is a great location to build some easy storage shelves that will greatly increase the amount of square footage that you can use for storage. While I do have a nice shop setup you can complete this project with just a few common tools:
The exact materials will depend on your situation. You will need:
Keep in mind that not all structures or garages are created equal. Before starting on a project like this make sure your garage can indeed support weight from below. If you are unsure consult a professional.
It's always best to establish a plan of attack for your project. Figure out exactly what is needed and the order in which you will complete the project. There is no perfect planning method that works for everyone but I tend to use SketchUp to make sure I have all my ducks in a row before I start. Here's an overlay of my plan. The grey lines represent 2x2 boards. The orange lines represent the vertical 2x4 supports. And the green area represents the plywood shelves. Then it was time to get all the crap out of my way to start in on the project.