just gonna ask do you use tablet?
Yep, an 8x6 WACOM tablet. It's small but it gets the job done!
It'd be really difficult to paint digitally without one. I once knew someone who claimed to paint on the computer using a mouse (and with an additional program that supposedly creates pen pressure on the mouse), but she was actually an art thief, so I'm not sure I trust her word on that...
Though, there are some amazing people like norli on deviantart who can draw beautifully with only a mouse ( http://norli.deviantart.com/art/Charms-43514418