It's fun cultivating friendships with the local farmers. Also, produce that's in season is much cheaper than an out of season item. If you have limited time, a trip to the supermarket will be easier. Therefore, you should be somewhat familiar with the following charts before you buy. In general, Spring is the early season with lettuces, asparagus, and broccoli.
Summer is berries, tomatoes, pitted fruit, and corn.
Fall is the harvest when everything is abundant. Traditionally, winter is root vegetables and citrus fruits. Here is a seasonality chart by month on what is in season for that particular month. A good familiarity with the chart will help you in purchasing high quality, reasonably priced produce.