If one gets behind in planting or can only find leggy tomato plants here's something that one can do and get great results with them. Plants them on their side.
This can be done with non-leggy plants as well. It can set the plant back some to do this but in the end you'll produce more roots for the plant (see below). The increase in roots will have several benefits such as more nutrient uptake and better drought resistance. Also in northern areas the roots will benefit from being located in a warmer part of the soil profile.
One can also bury the stem straight down instead of on its side. University research in Alabama and Florida found that planting stems straight down with the root ball in deeper (and cooler) soil can improve fruit set in hotter weather. It's probably best to do this in southern areas and trench plant in northern areas (for more warmth).
If does the trench planting method make sure to place a tag/stake near the rootball so you don't cut the underground stem or disturb roots when cultivating.
These pictures were scanned from the book "Dick Raymond's Gardening Year" (ISBN 0-671-50973-X) published by Garden Way Publishing. I also highly recommend "Joy of Gardening". Any of Dick Raymond's books are well worth finding if still in print. They are simple and every informative. (NOTE - this is a non commercial site so images are for educational purposes only and not to be reproduced or copied for any other reason).
here are the results of trench planting.