I was just arguing with my wife about this as she wanted some fresh garlic while the plants aren't quite 'ready' yet!
You can dig the bulbs any time now, but for really ripe bulbs leave them until the foliage has turned yellow and started to die down. Not too long though or the stems will fall off and you will forget where they are!
Dig them up carefully and store them. A Frenchman told us last year to remove all the outside papery skin from the bulb before storing as otherwise this would make them rot prematurely.
Leave the bulbs in the sun for a few days once they are dug to thoroughly dry out which again will help with storing and hardens the skins.
I'm sure you know that the only time to plant garlic to get decent results is the previous autumn, from October onwards, as the cloves make most of their root growth during the winter. Spring sowing will only produce mediocre results.