Stake your tomato well. Whatever method you use to stake your tomatoes make sure it will hold the plant. A good stake or cage will prevent the tomato from coming in contact with the soil and allow good air circulation around the plant to minimize fungal diseases. Traditional tomato cages will eventually become too heavy with the weight of the fruit to stay up so another method is better. Try using heavy duty stakes, heavy gauge wire cages with T posts to stake them up, the Florida weave method, livestock panel 'A' Frames or overhead supports with string lines for support.
Fertilize appropriately! I always hear of someone who goes out and fertilizes their tomatoes intending to get good growth and production. What actually happens is good growth and low production due to a high nitrogen fertilizer. Nitrogen will produce leaves and branches but not fruit. Take a balanced approach or lean toward the potassium and phosphorus part of the NPK rating. You don't want a 20 foot tomato plant with only 2 tomatoes! Organic fertilizers have lower amounts of NPK and feed the soil which is the best approach. If your soil is healthy your plants will be too. Artificial fertilizers feed the plant right way which will require that you continue feeding the plant to keep it growing nicely. When the soil is healthy the plants have what they need and use the nutrients as needed.
Prune correctly. With tomatoes you want to reduce suckering. Suckers are the little branches that begin to grow from in between other branches. You can let these grow but if you do your plant will grow lots of branches and have smaller fruits. The suckers also decrease air flow around the plant and increase the odds of fungal diseases. If you see signs of disease remove these branches and destroy them - do not put them in the compost bin. It's also a good idea to clean your pruners between plants as you can easily spread disease from plant to plant.
Blossom end rot happens very frequently to the first few fruits on your plant. Try not to worry about it too much and just remove the fruit. It's caused by a calcium issue in the plant. Calcium is used to form cell walls in the fruits and without enough calcium the walls break down and rot away the fruit from the blossom end. Either the plant isn't getting enough water to transport calcium from the soil, the plant is getting too much water to transport the calcium, or the soil doesn't have enough calcium in it. Most likely it's not a soil issue as there's almost always lime available but if it is an issue you can amend with lime or bonemeal. These will take time to break down into forms usable by the plant. Try to keep the watering schedule regular, water deeply, and do not overwater. Too much water will also cause the skin to crack.
Use these tips to grow some of the best tomatoes ever! Remember the best tomato is always the one YOU grew.