Is there a plant more confusing to prune than clematis? Not only are there numerous types but they are all pruned differently. Fortunately, there is a helpful resource and it is Linda Beutler's wonderful book "The Plant Lover's Guide to Clematis". I have referred to this book so many times that it is literally coming apart. In the book, the author lists all the cultivars (well, not all but close) and tells how to prune each one.
Our largest clematis are on the front gate arch and they were spectacular this year, blooming for a record amount of time (I am crediting the mild temperatures). On one side is 'Jackmanii Superba' and 'Madame Julia Correvon' is on the other.
In the photo above, 'Madame Julia Correvon' is on the right. It is not as strong a grower as 'Jackmanii Superba' but I expect it to catch up next year. After blooming, it is recommended that it be cut back half-way and you will have more blooms from autumn to frost.
Of the two, 'Jackmanii Superba' seems to be the most vigorous grower. In the book, 'Jackmannii' is listed and the instructions say to just cut it back in late winter or early spring. No mention is made of cutting it back half-way after bloom, so I just cut off the spent blooms.
The end result is a much neater archway. I fertilized with Jack's Blossom Booster and await more blooms later in the season!