What you'll need
 

Make a plan, get the picture

As with all jobs in car restoration: first make a plan. Before you buy anything or start any work, define your aim. What quality of workmanship do you want to achieve? My first seat cover looks really nice and some friends have already admired it, but I can see my shortcomings. There are some folds which don't look perfect, the piping of the base is a little bit thinner than of the back and the flutes are not perfectly aligned. But I like it and I don't have to deal with anybody else who hasn't delivered good work to me and I enjoy working with leather.

If your leather is just hard and a little cracked consider also treatment and repair. It's usually much cheaper and less time consuming than sewing a new set of seat covers and conserves the cars originallity. Even seat covers beyond repair should be treated with hide food to have nice and soft templates to work with.

Ok your fingers are itching now and it's time to get the seats out of the car and into the workshop. Take your camera and your sketchbook. Photograph every part from different angles and sketch the pattern of your seats. I recommend to start with the base of a front seat . It's the smallest and least complicated part of the seats. Remove the clips and pull the sides of the seat cover up. The piping is glued to the foam. Cut carefully with a sharp knife to preserve the foam and your old seat covers. Number the parts on the back and mark them on your sketch accordingly. Nothing worse than spending hours to puzzle out how the parts are assembled at the end.