A good crop of tomatoes is not just an accident. A bit of ‘TLC’ will be repaid

Watering is key to growing a successful Tomato. If a Tomato dries out the skin quickly thickens. If you water inconsistently the skin splits. Irregular watering can stop the uptake of Calcium which causes Blossom-end rot making the bottom of the fruit brown and inedible.

Feeding Tomatoes will increase the yield. All that rapid growth and fruiting takes a lot of nourishment. If you are growing in pots, grow bags or containers all the nourishment is provided by you. Provide a high potash feed weekly, increasing the frequency the larger the plant gets in July and August. If the leaves start to look pale, discoloured or yellow it hints at feeding deficiency.
To encourage more roots plant part of the stem as roots will spring from the buried stem.

Training your Tomato up a cane or string with regular ties to support the weight of fruit. 

Cordon grown tomatoes need to have all the side shoots nipped out to focus the growing strength into providing fruit. Pinch out the growing tip after 5 trusses of fruit have been set. Bush Tomatoes trail and tumble and you can leave the side shoots on but still give support. Remove some bottom leaves too allow air and light to get to the lower trusses of fruit to help them ripen but always leave leaf at the top of the plant for photosynthesis. Low sun levels will mean slow ripening.
Alternatively try training up a wigwam.
As soon as plants are growing create a wooden frame to keep fruit off the ground.

Pests such as white fly can be controlled with sticky flytrap paper or frightened off by planting pungent Tagetes or French Marigolds. Warm humid air can cause a fungal blight infection which can only be treated chemically. Change greenhouse soil after each crop.

Ripening
Put green tomatoes min a box or drawer with a ripe one or an apple. the ethelene give off ripens the green fruit.

Summary – Water daily, feed weekly, support the weight and be on the look out for pests.