Have you ever grown tomato plants that just became a complete mess by the end of the season, where there was far more plant than fruit? Ever notice that most tomato plants will get 7-10 feet tall, but you can't buy tomato cages that are much more than 5 feet tall?
I've been searching the internet on the best ways to grow my tomatoes vertically without a big mess, and I've decided that this year I'm going to use the "string trellis" method this year for 5 of my 6 tomato varieties. Why 5 of 6? Well, 5 of my tomatoes are considered to have "indeterminate growth", which means they will continue to grow and grow until the end of the season. Most non-bush tomatoes are like this. The only "determinate growth" tomato I have is a Roma, which will not get more than 6' tall.
Another thing I've never done is prune my tomato plants, and apparently, pruning your tomatoes will allow you to grow them vertically more cleanly and the plants will produce more fruit. If you don't prune your tomato, it will spend much more energy growing new stems and new foliage, and less energy growing fruits.
Here is a fantastic video from someone on youtube named FrontPorchFarm that makes it really clear on how to properly string trellis and prune - or sucker - your tomatoes: