Tomatoes are generally heat-loving plants, some of which tend to grow tall, so give them full sun, rich soil, and a trellis or stake to grow on.
Plant seedlings in the garden after all danger of frost is past, or plant a bit early and protect crops with row covers.
If your soil is rich and well amended with compost, you won't need to fertilize. But if it's nutrient-poor, apply controlled-release complete fertilizer once at planting time; if you need to feed the plants later to boost growth, use a relatively mild plant food like fish fertilizer. Too much nitrogen makes plants grow leaves at the expense of fruit.
There's one more thing to consider if you want really great tomatoes: water management.
Water regularly but sparingly
At Gary Ibsen's 2005 Carmel TomatoFest in Carmel Valley, California, there were two plates of 'Early Girl' tomatoes on the tasting tables. One was among the sweetest, most intensely flavored fruits at the show, while the other - its genetic twin - was an unremarkable also-ran.
What made the difference? It all came down to culture. The unremarkable one was grown conventionally, while the sweet one was dry-farmed (a technique possible only where the ground retains enough moisture to support the plant all season long with no irrigation-like some areas near the Northern California coast, for example). Dry farming has several advantages. It keeps water off the leaves so plants aren't as susceptible to late blight, it concentrates sugar in the fruit, and it minimizes fruit splitting, which results when late-season irrigation pushes pressure inside the fruit past the breaking point. Among the disadvantages, dry-farmed plants produce fewer, smaller fruits than conventionally grown tomatoes.
Not every gardener can dry-farm, but the lesson is clear: If you can manage to water regularly but sparingly, you'll get sweeter, split-free fruit. Drip irrigation can help you achieve that.
Though tomato plants can (but don't usually) encounter many minor problems, there is one major problem that can cost you your whole crop: late blight. Caused by the same organism (Phytophthora infestans) that brought about the 19th-century Irish potato famine, it usually shows up around harvest time, transforming plants and fruit into disgusting blackened waste.
Tomatoes become infected when airborne spores land on wet plants, so your first line of defense is to keep leaves dry: Flood or drip-irrigate your tomatoes and never use an overhead sprinkler. To keep rain off leaves, some gardeners cover their rows with clear plastic tents. Fungicide prevents and controls late blight.
Next: A foolproof system for growing tomatoes