If your garlic cloves have started to sprout, do not worry. You can plant them. The best time to plant them is after the first frost. Garlic, unlike most common garden vegetables, needs frost to successfully complete its growing cycle. Ideally, you want to plant the garlic while you are still able to work the soil, but while it is too cold for the garlic sprouts to push their way up through the ground. Planting after the first frost helps ensure optimal conditions.
Dig up the soil where you intend to plant the garlic clove. Turn it over and break it up as you dig to a depth of 8 to 12 inches. Garlic requires full sun to do well.
Dig some compost into the soil. Reserve a little compost for later.
Plant the garlic clove in the soil, about 2 inches deep. Make sure the pointed end of the clove (not including the sprout) is facing downward.
Cover the garlic clove with soil, then with a few more inches of compost.
Water occasionally, but not deeply. Keep the area around the garlic well weeded to prevent competition for vital nutrients.