Pruning Group 3 Clematis can feel a bit brutal. The key is to be brave.
Group 3 Clematis include the later flowering clematis, whether they be large-flowered hybrids such as Gipsy Queen or the smaller viticellas, orientalis, tangutica and texensis groups. The key is that these plants all flower on the new season's growth.
Prune Group 3 clematis in February in the South and in early March in the North. The process is almost the opposite of pruning Group 2 plants. Instead of starting at the top of each growth and working down, you start at ground level and work up until you reach the first pair of good, strong buds. Prune just above that. Repeat for the rest of the plant.
This process means you remove the vast majority of the plant. If you do not do this, the base of the plant develops a rather ugly, leafless, leggy appearance. So, unlike Group 2 pruning, be brave. Prune early and prune very hard.
What I have written above is text book stuff. The late Christopher Lloyd, who was a great clematis man and wrote one of the definitive works on the subject, walked me round his garden at Great Dixter in about 1988 or '89. He was a charming, very funny man who tended to think outside the box.
He hated the way Group 3 clematis looked after they had finished flowering, and he had a point. They flower themselves into the ground. So he followed the rules except that he pruned them in November.
In a fierce winter, the new growth in February would be cut back by frost, but new growth appears and flowering happens as if nothing happens. Do this and your garden will look tidier. The deal is that you recall one of the truly great gardeners when you do so.