Decent projector installation

Ah, the quest for a decent projector installation continues. Easy you'd think, buy a bracket and stick it up. OK. So what about the cables? How and where do I run them, what do I use, who do I use to do it? Having done a bit of this sort of thing myself in a previous job I have been disappointed by the installs that we have had done at school so far. With another classroom due for a ceiling mounted projector, sound etc. soon, I think I might do this one myself and see how it goes.