To get the best tomatoes, pay attention to watering and fertilizing your tomato plants.
Tomatoes need a good amount of water, and they produce better with deep watering. Deep watering is when the water sinks deep into the soil, not just remaining at the surface. How you apply irrigation water does impact how deep the water will get.
Some guides have advised that tomatoes need about 1 inch of water per week. (See Tomatoes publication from Kansas State University Extension Service, and University of Minnesota Extension Service article Growing Tomatoes in Home Gardens).
Water can come from rainfall or from irrigation (that is, watering from a hose or irrigation system. When watering, it's best to direct the water at the soil surface, and be mindful to allow the water to soak deeply into the soil. You may need to water until it starts to run off and pool at the surface, then stop for a few minutes to allow it to soak in, and then resume watering.
Another technique is to set the water at a trickle or slow flow rate and set the end of the hose near the base of the tomato plant. The trickle allows the water to soak in gently. I find it helpful to set a timer on my smart watch (you could also use your smartphone) to remind me to move the hose every 3 minutes or so.
You can consider using a soaker hose. You can position it among your plants and leave it there through the growing season. Attach the hose to the soaker when it's time to water. Be aware that soaker hoses don't always deliver consistent water through the entire length of the hose - in other words, the plants closer to the hose connection may get more water than the plants closer to the end of the soaker.
It's not just the amount of water. Tomatoes produce the nicest fruit when the water is consistent. The tomato fruits are impacted negatively if the soil dries out and then the plant receives a flood, and if this pattern repeats over and over again. Inconsistent water can cause the tomatoes to and to develop blossom end rot.
You can only partially control consistent watering because you can't control rainfall. Still, it's worth the effort to try.
To encourage consistent moisture at the roots of the tomato plants,
Tomatoes require fertile soil to produce well.
Before planting the tomato transplants/starter plants, add a general purpose garden fertilizer to the garden soil, following the instructions on the label.
As the plants grow, sidedress the plants with additional fertilizer. The guides reference above suggest fertilizing 3 times as the plants are growing:
I'm usually not so precise about this schedule. It helps me to remember to start the time above and then once a month for 2 more months.
I recommend you use a fertilizer formulated specifically for tomatoes. The fertilizer needs the right amount of nitrogen, because too much nitrogen encourages the plant to grow leaves rather than fruit.
I prefer organic fertilizers because they feed the plants more slowly and consistently. It's difficult to over-fertilize accidentally with organic fertilizer.
Tomatoes do take a little more attention and understanding to get them to perform their best. Since they are the most popular garden vegetable to grow, obviously people believe they are worth the extra effort!
Even if you don't follow these instructions to the letter, chances are you will successfully grow some tomatoes to harvest. Nudge your gardening techniques to get better every year - it takes time and you will see results. This is how we become better gardeners!