Step 1: The tomatoes!
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.