Year-round production is a little hard to manage. It depends on the life-cycle of the plant in question and the amount you intend to harvest at any one time. Lets take peas for instance. Normally they have a life cycle of 45 to 60 days. You should decide how many peas you want to harvest for food and how many you want for seed. The ones for seed are going to take longer (perhaps up to 90 days) so place them someplace were they are not going to get in the way. The ones for food should be spaced so that they are not too crowded. This will allow for room to plant the next crop in the same place. Wait until they have bloomed and you are sure that you don't have any diseases in the crop and then plant the following crop (about 30 days). When the first crop is about finished (app. 60 days) the next one should be blooming. Carefully pull the first crop and plant the third crop, and so on.
If you're going to employ rotation (highly recommended) then you can plant them closer together and just plant the following crop in the next area. Of course the rotation is easier to manage with the seed crop. After the onset of seed pods, plant the next seed crop in a new area. When the seeds have been harvested from the first crop, plant the next veggie.
Offered by Roger.