Tomatoes and peppers need to be grown from seedlings first. Tomatoes are nightshades and you have to avoid growing other things around them or you'll poison yourself with the nearby crops. Peppers take forever to grow and the gophers end up getting most before harvest. Best to grow 50+ in a bucket or two in coconut core. Plant them all early in the season as seedlings taken out of the coconut core, then when they get large enough for the gophers to go after them, start transplanting them from soil to pots.
Potatoes, get some large IKEA bags and poke holes in bottom with soldering iron. Then line bottom of bag with gravel. On top of gravel mix a third dirt, potting soil, and fertilizer (horse poop). Put in some potatoes and water regularly. Don't leave in area that will overheat.
Easiest plants to grow are lettuce, spinach, radishes, carrots, and onions. Plant these directly in soil. No need for growing from seedlings. Lettuce will grow year round in warmer climates and can be harvested in a month or two. Same for spinach, though it doesn't like the cold quite as much. Carrots can handle some mild freezing as well. When their leaves grow out, throw some dirt on them. Do this at least a couple times as they grow for large carrots. Onions are not liked very well by gophers. They will eat them, but they'll only take one bite out of a big onion before looking elsewhere for food. It's best to plant onions at the edges of your garden to keep the critters out. Some onions can grow to 3 lbs.
When I grow onions, I usually also grow cilantro for tacos. Crack the seeds in half. Put them on a paper towel. Wet the paper towel with warm water. Place the paper tower in a zip lock bag not sealed shut in a warm, completely dark location for a couple days. Then plant in soil, potting soil, or coconut coir. In the summer, grow cilantro in a partially shaded area. Too much heat and it will bolt.