Not pruning as such, just a tidy up at the lower stem. Peel (or trim) old discoloured growth at the lower part of plant. Doesn't require a tidy up very often at all.

I am fascinated by the number of questions on cordylines. Are they particularly difficult to grow? I wouldn't ever want one as I don't like this shape of plant but I have just noticed how often they come up on this site and I am wondering why......

Cestina - On the contrary, Cordylines are not difficult to grow! They can live in almost anything (they do particularly well in my clay filled garden) and require very little care (apart from watering obviously!)
I agree with you on how often a question pops up but it does tend to be from guests, so they probably aren't aware of the care (or lack of!) it needs.