Start by taking a soil sample and sending it to the University Extended Coop. I say this a lot but if you start with the right soil your going to have the best crops with less problems with disease and pests.
Fill out the paperwork including what you plan to plant to get the best results. Then plan on a nice talk with the master gardeners at the coop to explain how to use the information you get back.
Other than that keep your veggie garden
weed and pest free. Rotate the veggies so that the soil doesn't get depleted. Plant a cover crop in the winter to rejuvenate the soil and keep it from erroding. And companion plant when you can.
Good luck with your garden.