HOW TO SKIN - HELP (EXPERIENCE NEEDED)

I'm new to the whole XBMC front-end/HTPC thing but I love what I see so far. I'm building an HTPC very soon and I will running xbmc. I've tried some great skins but I'm interested in either creating my own or using "confluence" and tweaking it. I have no idea where to start. Can anyone help me out? it would be greatly appreciated.

Thanks