Welcome. No matter how long, we keep learning and getting experience.

Q: Are you just growing in pots or also in beds ?

Q: What your growing conditions are like ? Sun, shade, summer temperatures, season length ???

For Pots/containers :

For better production and ease of maintenance, bigger soil volume is better. It should provide for a good root mass, better moisture and nutrient retention . Minimum size being 5 gallon for smaller plants, but 10 + gallons is better.

Use only "soil less" potting mix, with good structure. .

With soil less potting only use synthetic fertilizer.

Think about supporting your plants from the time you plant them. Cage ? stakes ?

Implement fungi prevention schedule from day one, every 10 to 15 days.Do it as "preventive" measure rather than waiting and trying to fight the diseases.

There are many aspects to growing tomatoes.

Wait for other comments.

Sey

My most valuable lesson in 2015 was about fertilizing. My normal method in the past was to use a light 10-10-10 about 2 weeks after planting, then another dose of the same in mid-summer. Our summer was very hot and pretty dry this year, so I skipped the 2nd fertilizing. Consequently, my production quantity was pretty low. In hindsight, I think I should have used an organic such as tomato tone for regular feeding during the summer.

John A

Its worth the trouble growing from seeds. I used to buy plants from local nurseries. The selection was so limited. I had a good harvest last summer growing "new" varieties that I discovered here. These tomatoes were available from seed only. Plus, this gives me something to do in late winter, keeping me off the streets.

There can't be too much sun. At least not in this zone. Last summer I had a dozen plants in a row. The plants in the end of the row were shaded in late afternoon. The decline in production was obvious. This year the row will go east to west at the far southern edge of my garden. Each plant will get 8 - 10 hours of full sun.

Growing my plants on the 5' fence which surrounds my garden worked much better than stakes or cages.

Grow when whiteflies are not around or suffer the consequences.
Keep tomato seedlings away from rain and wet.
Mulch.

Start earlier. Last year I had tomato plants started in the fall (October?) and then again around Valentine's Day. Much too late for my growing seasons. Start in July and December means tomatoes are able to get done in time, provided the weather isn't crazy. My tomatoes from the fall still aren't ripe yet thanks to El Niño, despite my best efforts....