Original pencil drawing before applying colouring in Photoshop CS5. Which usually involves using Burn and Dodge on a R153 G134 B117 (Light Cool Brown) coloured layer Multiplied over the Pencil Artwork. It helps to change the size of brush via the keyboard as you 'paint' and to set the opacity of the brush to around 40% to build up layers. My favourite textures, like fur and concrete, are then Overlayed as well as layers which are flattened and Cut Out and Poster Edges filters applied, using Overlay in the Layers palette.
It's also worth looking on the net for custom texture brushes for Photoshop. Some really simple designs are extremely effective, especially when they 'rotate' in their pattern. Lost & Taken is one of my favourite sites for Texture inspirations.
Basically I throw everything into the mix. I try not to use Undo if I can help it, if a layer combo doesn't work I tend to turn the opacity down to 8% and flatten it into the image any way. Mistakes are part of the process, a bit like 'physical' art.
My colouring secret that I can't tell anyone involves the colour R54 G47 B45 (Darker Cool Brown), applying Lens Flare and Gaussian Blur and then using the Overlay filter. It really makes the colour on the page come alive. But like I say, It's a secret and no one will understand my blabbering on enough to make it work for them.