I had calculated when planting to grow enough to get us through to the next harvest and also allowed enough to be used as seed for the following planting.
It is a great crop to grow. Basically you get a bulb from planting a clove, so save ten cloves for seed and you get ten bulbs (approximately 100 cloves of garlic). I figure that I have only had to buy the seed the once and from now on I'll just save from the previous harvest for planting and it will go on and on year after year unless I lose a whole crop due to disease or something. This is basically the principle behind seed saving, and if you are going to start anywhere on this process then garlic is a good place to start.
I've found it really easy to grow. It's a long growing season but once it's planted you just need to keep it watered and you should be right. I can't imagine that there would ever be any pest problems.
And, it tasted better than the generic white bulbs that you buy from most places!