there are a lot of handy tutorials out on the net if you search for them. i like checking out deviantart personally, you can also download photoshop brushes and stuff from there too. a lot of comic book artists have accounts on there so it's always fun to check their stuff out.
if you use layers, if you mess up a layer, you can simply delete it without deleting everything you did. you can keep the lines on one layer, the background colors on another, textures and lighting on another, etc.
i'm a novice at best but its fun to tinker with and try out, which is why i wanted to revamp a new coloring book for 2010. i think i still will do that, so if anyone has requests, throw em at me.