Start with seed garlic from a garden centre, a nursery, or a seedsman. Grocery bulbs are grown for eating, sold with no promise about how they will grow, and two extension guides say plainly that they are not planting stock. Seed garlic is also where named varieties come from, which is the only way to choose between a hardneck and a softneck on purpose.
Clove size is the other decision and it is close to a straight line: the larger the clove, the larger the bulb it makes the following summer. Plant the biggest cloves and eat the small ones, and re-select every year — the largest bulbs give the best planting cloves, which is how a variety improves in a garden instead of drifting down.
The site should drain, and it should see sun. Garlic sits in the ground through the wettest part of the year and rots in soil that stays saturated, so heavy clay is worth raising: Cornell's home-garden guide puts the crop in beds two to three feet wide and ten to twelve inches deep where the ground is heavy, and Wisconsin's warns that bulb expansion is impeded in clay that dries out.