Default Debranding/Custom Rom question

Hi,

How do I go about debranding & customizing a rom (either using a stock rom or custom rom as base). I have a stock rom (zip) branded orange UK and I firstly want to remove the network branding stuff, then maybe add a few extras. I have cwm recovery installed so I want to be able to flash it as a zip.

Please can anyone outline the procedure please?

Thanks