You can plant members of the nightshade family after garlic. Garlic is a light feeder and requires a small number of nutrients. You can follow up a garlic harvest with peppers, tomatoes, and potatoes. These are heavy feeders and require more nutrients different from garlic.  Rotation of plants is important. Growing the same plant consecutively can result in poor soil quality and can leave pests and fungus in the soil. The unique benefits of these plants are they deposit some nutrients back into the soil and are fast growers.