Do you know the name of the Clematis?. Some of them need none or little pruning, some need a little pruning now(ish) and some need very heavy pruning in February.
Lack of flowering is often due to lack of water, it has been a very odd season. Or lack of food, Clematis are very heavy feeders. Give yours a feed of Rose Fertiliser in February. Maybe able to help more when we know what you are growing. :)