Knowing that fruits and vegetables are perishable, buy only the fruits and vegetables you know you will eat. Find a nearby local market and purchase only the necessary foods that you will eat throughout any given day. Each week try and expand your horizon by trying a new fresh fruit or vegetable.
I feel one key to getting good fruits and vegetables at a farmers market is to become a regular and get to know a couple of the vendors. In my experience most of the vendors at a farmers market are eager to talk to the customers and promote their goods. By building a relationship with a couple farmers they can get to know your tastes and help you pick out the produce you'll like the most. Besides, if you're a regular someone may even keep a particularly good batch of strawberries under the table for you.
I would say you can’t really go wrong shopping at the farmers market. If you’re planning on visiting weekly, become familiar with the consistent vendors and aware of any new vendors. Be sure to stroll around and notice new products that may arrive, such as organic health care products. Perhaps taking the time to seek out farmer’s markets in neighboring towns/cities will broaden the selection for locally grown produce as well.
Some tricks to picking out fruits or veggies at your local farmer's market are to know what is in season. That way you know what to expect when you get there. Also, try and get there early so you can have the first pick without having anything being picked over or sold before you get there.