Keep only the items on your desk that relate to your current projects.
Clean out your files, but before you go through the expense of buying more file cabinets and folders, purge all unnecessary paperwork and materials.
Don't waste time searching for papers. Keep all paperwork that pertains to a certain project together in one large folder.
Don't overstuff file cabinets. Leave enough room so you're not using all your energy to get a piece of paper in and out.
Add shelving for reference books and manuals. Add space extenders in desk drawers. Use stacking bins.