Pruning Group 2 Clematis is nearly as easy as pruning Group 1 plants (where you do not do anything most of the time...)
Group 2 Clematis (sometimes known as Group B or Type B clematis) include all the early, large flowered hybrids. These will produce their first flush in May or very early June.
Prune Group 2 clematis in February/early March. By then their buds will be swelling and green and easy to see. If the winter has been very cold, growth will be delayed in which case you can prune in early/mid March instead as it is easier to see what you are doing.
The exercise really involves a tidy up of the plant:
The most famous member of this group is Nelly Moser, but it also includes the likes of Lasurstern, Vyvyan Pennell, Mrs Cholmondeley and Duchess of Edinburgh.
Group 2 Clematis are the "mid-season" flowerers. Later than Clematis montana Tetrarose for example, but earlier than Gipsy Queen.
Group 2 is unlike the early flowering (Group 1) which need no wood removing, and therefore no pruning, as their flower buds were fully formed the previous year. Instead, Group 2 clematis form their flower buds in late autumn and early spring.
Group 2 clematis are sort of half and half clematis. Some of the wood needed for this year's flowers was produced late last year and some grows early this year. So it needs cleaning up, but no severity. Be gentle. With Type 2 clematis, less is generally better than more and you should only ever be heavy handed when the plant is too large or has a main growth where you don't want one.