In late summer I try to set aside a Saturday morning to can a dozen or so pint jars of tomatoes. Canning tomatoes does not require a lot of fancy equipment and for one morning's worth of work, you'll have plenty of jars of this beautiful fruit all through the winter.
Step 1: The tomatoes!
I am lucky to have a wonderful Farmer's Market in my neighborhood, and if you have one in your area, that is the best place to purchase the tomatoes. You can be sure that they'll be local, fresh, and often organic - and you can usually get them for a much better price than at the supermarket.
In my geographic area, tomatoes do not really come into their full bounty until mid August. And when they do, I connect with a local seller, place my order, work out a price and then plan to pick them up the following week. I usually buy a basket of tomatoes which I think is about a half bushel. Always look for fresh, unblemished, and fully ripe tomatoes.
The best canning tomatoes are Roma tomatoes. The are small, oblong and firm-fleshed. As a result, they hold up very well in the canning process.
Once you have picked them up you should plan to can them as soon as possible. My Farmer's Market is on a Friday and I always plan to can the tomatoes the next morning. No need to refrigerate them - they'll be fine on your kitchen counter overnite.
No matter how many times I have done this I always follow the Ball Blue Book Canning Guide step by step. I encourage you to do the same thing.