tl;dr Plant deep. Remove lower leaves. Water. Fertilize. Support. Pinch.
My friend Harvey knows a lot about plants; it's his business to take care of them. Here are his recommendations for tomatoes:
Use any balanced fertilizer once a week. He recommends Jack's 20-20-20.
Tomatoes do well being "constricted", so keep them in a 4-6" pot until they're ready to be transplanted.
A 5-gallon bucket with holes in the bottom is a good planter for tomatoes.
When you are ready to transplant, remove the bottom 3-4 inches of leaves and plant the seedling deep in the ground so that those lower inches of stem are covered by dirt.
As the tomato plant grows, keep the bottom foot free of leaves. This will let the sun reach the soil and warm it better, and will also reduce disease spread from the soil to the leaves.
Stake your tomatoes. In addition to a cage you might add four or five six-foot bamboo stakes. These tomatoes will grow like crazy if you feed them well; be prepared with good support. Harvey gets hundreds of cherry tomatoes from a single plant.
Tomatoes grow a lot of "suckers": new branches that grow out of the tomato's main stem, just above a leaf branch or side stem. The more branches, the bigger the plant, and the more energy goes into growing stems and leaves -- and ultimately, more flowers and fruit. However, you need to make sure that the plant doesn't grow so big that there is not enough sunlight, water or food to support it. You control its growth by pinching off those suckers -- grasp with your thumb and finger, and cut through the young shoot with your fingernail. By pruning you are allowing the plant to concentrate its energy on fruit production. Think of yourself as a sculptor, being aware of the resources available to the plant. I'm more aggressive with the heirlooms than the cherries, just because the heirlooms seem to need more coaching to focus on the fruit. Do some googling to find out more! Note: determinate tomato plants (in our case, the Defiant variety) do not need pruning.
U Mass Amherst has some great advice for growing tomatoes. You can read it here. A summary:
Choose a sunny spot.
Add organic material to the soil.
Fertilize enough but not too much.
Water enough but not too much.
Keep an eye on soil pH.
Have your soil tested (once labs open after covid-19!).
Choose flavorful varieties.
Start with good seedlings.
Support plants in the right way.
Let fruit ripen on the vine.
Whew! That is a daunting set of suggestions. True confession: I make lots of mistakes, but still harvest a bunch of tomatoes. Don't be discouraged by all the advice: if you have an inclination to learn more, do so! But, if you don't have time and attention, just plant the seedling, water it, fertilize it, and enjoy. The varieties that we have selected generally do quite well in containers in Cambridge.
Some vocabulary from the U Mass Amherst article:
Mulch is material spread on the surface of the soil to keep the soil cool and moist. This is especially helpful in containers that can dry out quickly.
Tilth is the physical nature of the soil, in the context of growing a crop. A good soil will have a variety of pore sizes so water and air can get through, and roots can grow, and it will crumble when you pick up a handful. Earthworms and organic material help with tilth.
Lime is a soil additive made from limestome. It supplies calcium and increases the pH of acidic soils. There are other ways to supply calcium without affecting pH.