Step 1: Check Blades
At least once a season, you'll want to replace or sharpen blades on any tools that cut or dig. Your tools' blades see a lot of wear. Use files to sharpen digging tools and to sharpen nicked or dull cutting tools.
Sharpen very dull hedge trimmer blades by moving a file away from and diagonally across the sharp edge. You want to maintain the factory bevel. Then decrease the angle slightly and hone just the last 1/16" of the blade with a sharpening stone. If the trimmer has a serrated blade, do not attempt to sharpen it. That's a job for a professional.
Most digging tools aren't sold sharpened, so you need to sharpen them from the get-go. As time goes on, the more you use your digging tools, the duller they get. File the working edge to a 45-degree bevel with a coarse file.
For a bow saw, use a triangular file to sharpen both sides of each of the saw's teeth to a 45- to 60-degree bevel. To keep track of where you are, file every other tooth starting at one end of the blade, then file the remaining teeth the same way, working from the other end. File toward the sharp edge.
Hone and maintain the sharp edge of all cutting tools with a medium-grit sharpening stone. For faster cutting, wet the stone with water or lubricate it with honing oil depending on the type of stone you have.
Clamp a pair of boards on the blade and lock it in a bench vise. This will keep you from having to keep changing the blade position in the vise.
Before you store your tools for the off-season, use a wire brush to remove surface rust and dirt. Wipe down the metal with light oil to protect the metal from corrosion, especially if you store such tools in a damp garage or basement.
You should wear heavy gloves when cleaning or sharpening sharp cutting tools. Wear goggles when using a wire brush to remove rust and dirt.
Step 2: Check Handles
Check your tools' handles for splinters, breaks and cracks. Smooth weathered, rough wooden handles with a medium-grit emery cloth — it won't tear as easily as sandpaper. The handles should be smooth enough to slide your hand along. If the wood is very rough, first sand across the grain in a "shoe-shine" fashion. Finish by sanding with the grain.
Wipe a dry handle down with a heavy coat of linseed oil at the end of the season to rejuvenate and protect the wood.
Sometimes repairing the wood is not a safe option. In these cases, it may be worthwhile to replace the entire handle of a favorite tool. For example, don't attempt to glue or tape a broken wooden handle. Use a ball-peen hammer or a block of wood with a nail hammer to knock the tool head out of the ferule on the handle.
Never strike a metal tool with a nail hammer. It may chip off a dangerous metal projectile. Always wear eye protection when using a hammer to make a repair.
Good job! As long as you properly maintain your garden tools, they should last a long time.