You need to know when your plant usually flowers if you can’t remember make a note of it this year. Spring flowering Clematis such as C. montana usually only need to be tidied up AFTER flowering. Reduce excessive growth & cut out any dead, damaged or weak stems.
Clematis which flower before midsummer should be lightly pruned now. This means checking long unwanted stems which are maybe heading in the wrong direction for your purpose, removal of tangled stems and old flower heads.
Its also time to prune late flowering Clematis. Late flowering generally means flowering after midsummer and applies to large flowered hybrids as well as C. texensis & C.viticella groups. Simply reduce last years growth to a few strong buds just above the base.