There are several opinions on ways to prune tomato plants. It depends on the type of tomato plant habit and the plant support you are using. Pruning is most helpful for indeterminate varieties of tomatoes. This type of growth can be pruned by removing all suckers. Suckers are shoots that form at the corners where the side branches meet the stem. The best way is to remove them while they are small by pinching them off. If they are bigger, you can use the pruner or very sharp knife.
Another way to prune indeterminate varieties is to prune only the lower 10’ of the plant, some inner branches for air-flow and any diseased branches to control the spread.
Determinate or bushy tomatoes are usually smaller and easier to grow. They do not require pruning, which can be detrimental to fruit production.