For a first time tomato grower I would recommend buying starter plants from a local garden store -- and I say local garden store becasue they are more likely to only stock the types that will do good in your area where as the big chain store many times stock things that don't do well in your neck of the woods.
There are also determinant and indeterminant types of tomatoes, determinate ripen all about the same time, indeterminate ripen throughout the growing season. If you are looking to make big batches of sauce, I would probably go with determinant - the lables should tell you what type it is or a good gardening website will also.
How to prep the soil -- really should have started last fall tilling in grass clippings and leaves, however read up on compost piles, you can start them any time, though they really get cooking in the summer: leaves, grass clippings, kitchen waste and many other things go into a composte pile and if done right will turn into great dirt. Having said that if you are starting from scratch come April or May, get yourself some bags of compost from the garden center and mix it in with your soil.
Do you know if you have a clay or sandy soil? either way you will have to amend it, just with different things.
Also many garden centers and most universities will test your soil and tell you what you need to add to make what you want to grow, grow better. If you don't mind chemicals - Miracle Grow really does work on tomatoes, if you prefer organic like I do, there are organic fertilizers that do a similiar job.
I will pass along a word of wisdom my father passed along to me. "We need to grow good dirt and then the dirt will grow good plants" By growing good dirt he meant composting and amending to soil to have the proper nutrients the plants need. I can't recommend enough getting your soil tested and knowing what the results mean and what to do with them. Your local garden center should know who does testing in your area and we have one local chain of garden stores that does free testing to get you in the door in the spring.(actually they get you in their door 3 times: once to pick up the soil sample bags and forms, once to bring them back for testing and once to pick up the results)
Another plug for a local garden store -- usually they have gardening expertise in your area, something the chains stores almost never have -- you'll pay a little bit more usually, but its usually well worth it: they specialize in gardening, its their only source of income so they usually only stock items proven in your area, they usually have expert gardeners on staff, and usually will stock plants at the right time of the year for planting in your area. And if you are having sick plants can usually help you out with them and if you saved your receipt will usually replace your plant or refund your money.
Here a decent article on soils
http://gardening.about.com/od/soil/a/GardenSoil.htm
One more thing to remember Insects are required in the garden - not all types of insects are pests, so get rid of your cans of insect sprays and also plant a few flowers near your veggies to draw pollinating insects -- my gardens really took off on production when I started putting a variety of different flowers in my veggie garden (different types draw different insects).
HeLp with an herb and tomatoe garden
