There are too many gardeners putting way too much effort into growing tasteless tomatoes. The progenitors of the modern tomato grow in poor rocky soil where days are hot and dry and nights are cold. Tomato plants are tough stuff. Do not coddle them. Unless they are in containers. The following information is for those planting common tomatoes (S. lycopersicum) in the earth, not in a pot or a bag or a raised bed on a solid substrate.
The best tomatoes come from plants that are very deeply rooted and made to suffer. Tomato plants will root all along the stem, which should be buried as deeply as possible when transplanting. Remove all lower branches to increase maximum depth and to keep foliage off of the ground. Mulch plants generously with grass to keep soil from splashing onto plants. Leaving just a few fronds at the top of a long bare stem when transplanting is fine. I promise. Water just until plants are established.
Assuming that you can plant to a depth of around 1' in moderately loamy soil, don't live in a desert, and have mulched generously, irrigation is not necessary. If your soil is very nutrient poor, amend it with azomite, kelp and fish bone meal before planting. Azomite can also be used to top dress throughout the season. Avoid nitrogen based fertilizers.
If your tomato plants are tiny and packed into small cells, consider transplanting them into larger containers to allow both the roots and top growth to develop further before planting into the ground. Do not stake tomato plants prematurely, as this will retard the development of sturdy stems.
If your soil is very shallow, plant horizontally to allow for maximum root development. Seriously. These plants will require more mulch and more water during dry spells, but should be healthier and more productive than plants just barely tucked in. Take care when weeding around these plants. Avoid using implements other than your hands, lest you risk cutting the subterranean portions of the plant. If you cannot imagine how one might plant tomatoes horizontally, look up “Trench Planting".
As your plants grow, be sure to continually pinch any lower branches that threaten to touch the ground. Whether you choose to prune suckers or not, you must keep foliage from touching the ground. Be ruthless. Stake, trellis, and religiously remove low hanging branches throughout the season. Once fruiting begins, withhold water and fertilizer. Too much coddling will make tomatoes watery and insipid. This is especially true for those tomatoes with sweet flavors and lighter colors. Make them suffer and they will be sweeter for it.