Determine how you wish to use the space. Besides a place to park the car(s), does it need to be a workshop? A storage center? For lawn and gardening equipment or for sporting goods? All of the above? To meet the various needs, create a floor plan and stick to it.
Get rid of things that don't work!
Sort, purge, and then decide the proper storage method for the treasures that you must keep. Clearly label both the tops and the sides of any storage containers you use.
Consider floor-to-ceiling possibilities for shelving, racks, stackable drawers, hooks, and pegboards.