Don't: Buy the Dirty Dozen
Not all vegetables are created equal. More specifically: Not all are grown to the same safe standards. Modern agriculture uses lots of toxic pesticides, and the residue from those chemicals remains on many foods even after you've washed them at home. Buy organic foods as often as possible to avoid residue of pesticides which some studies have linked to a range of health problems, from the reproductive to the neurological to the developmental. If you're on a budget and can't afford the premium price for organic food, focus your food dollar on buying organic celery, tree fruits (like peaches and apples), berries, sweet peppers, leafy greens and other foods that make the dirty dozen list. For more specifics, consult WhatsOnMyFood.org, which makes government pesticide residue testing data publicly available.