Northern California consists of many different climates. From the cool, foggy coastal areas that stretch from the Oregon border to the Monterey peninsula to the warmer inland valleys where tomatoes, almonds, apples and many other crops are grown in large farms, Northern California is indeed diverse. Soil near the ocean can be sandy, which gives it little nutritional value and water-holding capacity. Inland, in areas such as the Santa Clara, or "Silicon" Valley, soil is typically clay. In both scenarios, your vegetables will do best if you improve your soil with compost and other organic ingredients.
Consult "Sunset" magazine's Sunset Garden Climate Map to determine your climate zone. The Sunset Garden Climate map is used more in California for determining specific microclimate conditions than the U.S. Department of Agriculture climate zones map, which are the standard in the rest of the country. Knowing your exact climate zone will guide you in selecting types of vegetables that will reward you with the best success in growing them.
Dig up a scoop of unamended soil from the area where you plan to plant your vegetable garden to learn about the type of soil that exists on your property. Squeeze it in the palm of your hand: if it clumps together and remains in a tight ball, your soil is clay. If it is loose and sandy and does not stick to itself, it is sandy.
Measure your planting area. Mark the corners by driving stakes into the soil with your hammer. If you make beds that are no more than 4 feet wide, allowing for pathways between planting areas, you won't ever need to step onto the soil in your planting areas and the soil will remain well aerated and loose, which is good for plants. Also, you'll avoid wasting compost and other organic materials when you dig them in later.
Pull all weeds and any other unwanted plants from your garden site. If you dig these plants out with your shovel, it will help to loosen the soil and will eliminate the roots, which might grow back if they remain in the soil.
Amend your soil, whether it is clay or sand, by digging in organic compost. Spread a 3 to 4 inch layer of homemade or purchased compost of any type on top of the soil in your vegetable garden area and then turn it under with your shovel to a depth of at least 8 inches.
Plant the varieties of vegetables you have determined will succeed in your climate zone. Dig planting holes that are about twice as large as the root systems of your young plants and then set them into the amended soil and fill in around them with your soil-compost mixture. Water well after planting by running a sprinkler for 20 to 30 minutes and repeat watering every other day until plants begin to show signs of growth. From that point forward, most vegetables like to dry out before they get water again: usually, once a week watering is all they need.