If I could only tell you one thing about caring for your tomato plants it would be to not "over-loving them". Most of the problems that people have written me about resulted from crowding, applying too much fertilzer and/or too much water.
1 - Choose a site that receives as much sun as possible
2 - Choose a variety that does well in your area
3 - Avoid overcrowding
4 - Avoid over-fertilizing
5 - Avoid over-watering
Choose a site that receives as much sun as possible
Though tomatoes can grow in reduced light, production of fruit will be inhibited. Plants grown in low light conditions will often be spindly. Flowers may form but often drop with low light conditions. Plants located in more sun tend to stay drier which can help reduce the potential for some diseases
Choose a variety that does well in your area
Consult gardeners, nurseries or county extension agencies in your area to help select what varieties do best for your area. Other considerations when selecting are disease resistance, heat tolerance or days to maturity.
Yes you want more tomatoes but crowding plants together can reduce light levels and encourage disease problems by reducing air flow. One needs to look at what kind of variety they are growing (determinate vs indeterminate) and what method of growing they will use (ie. staked vs. caging) to determine the appropriate spacing.
One should fertilize. This is a "over-loving" issue: just because a hammer works doesn't mean a sledghammer will work better. In most garden situations one only needs to fertilize around transplanting time and once after fruit set has begun. Those growing in pots or sandy soils will require more frequent fertilizing. Blossom drop, excessive foliage and even some disease problems can be signs of too much fertilzer.
This is the other "over-loving" issue. Watering is important, especially when establishing plants. However, once established, tomato plants need only about a 1" of water a week.
Watering should be done such that it encourages deep roots by thoroughly wetting a soil so that water goes down deep, then allowing for a period of dry. This means it is better to water for several hours a week rather than watering for 30 minutes everyday. Over-watered fruits will often taste that way, watery. Foliage that stays damp is also more prone to disease.
Properly used soaker or drip hoses will allow for slow steady long watering and help keep foliage dry.