Well i just got some from my dad who says to pinch off lower unflowering branches now. Once flowers have gone you can start to feed them with tom plant food (apparently).
I always wait until 4 large trusses have set or 5 smaller ones then stop (pinch out the tops) of the cordon toms the bush cherry types I leave well alone as they can cope with producing 20 or more trusses if they are well fed and have even watering
I keep about an inch or 1 leaf on the side shoots. The leaves are making the food for the plant so don't snip too much. Regular watering and feding is also importanr.