Bonnie Orr, a master gardener, puts it in three simple words: clean, dry, and sharp (read his post in “In the Garden: Now’s the Time to Prep Those Tools for the Next Year’s Garden”). Tools with metal blades must not be left wet or covered with dirt. She advised to rinse them with hot water so they dry quickly.
Shears, knives, and other sharp tools must be sharpened before you put them away. In her post, “Practical Gardening: Cleaning and Storing Gardening Tools,” Margaret Rose Realy suggests the use of flat rat-tail file for sharpening as this works perfectly for hoes and forks. Once done, they must be cleaned of any remaining rust with steel wool.
Once you have successfully cleaned and stored all your garden tools, all you need to do is wait for next spring.