said by cdru :

If you are running your own lines and not being charged a per-drop fee, I personally would run 2 lines to the middle of every wall, or at least 2 runs per room on opposite walls, plus anywhere else where one might naturally need an network connection (behind entertainment center, at the wall phone, next to the toilet ). Terminate them all back at a patch panel and then you can only hook up the ones that you need.

Most network jacks can also serve for a 4 or 6-wire telephone cable as well, so you can kill two birds with one stone.

Don't forget about RG-6 too.