I found this wonderful tutorial on Tomato Pruning on VegetableGardener.com
My other tip for increasing your tomato yield is to tie your tomato stem a little tighter to the stake that helps to hold it up. The plant has a survival instinct to ensure that it fruits as quickly as it can under a little stress.
Be careful not to cut into the stem with your choice of tie. Avoid exposed wire, opting for shoelace, old pieces of panty hose, etc. If you use plastic coated twisty tie wire, be sure to check on it every couple of weeks to see if it may need to be adjusted.
Happy tomato season!