By this time of year the tomatoes are growing vigorously and need regular attention. At least once per week the side shoots should be removed, otherwise the plant will grow lots of extra branches at the expense of producing flowers and tomatoes. The image left shows what side shoots look like as does the short video, see below. It is because tomatoes are such a vigorous plant you need to  limit growth so that the plant produces more flowers. Removing the side shoots is one way, and also when the plant has made several sets, or trusses of flowers, and reached a good size around about 1.5metres or 5ft, stop off all further upwards growth by pinching out the top growing points and keep doing it. You will need to do this later in the summer when the plant reaches maturity. 

For now, just remove the side shoots and as the tomatoes are starting to flower start feeding. Not too much, just weekly, and step this up as the plant matures and produces more flowers and eventually tomatoes. Regular watering and feeding are key to producing good tasty tomatoes.  A short video about how to remove side shoots and more tips about growing tomatoes