References, art theory and some experimentation of what feels right! I use Corel painter for lineart and colouring, and Photoshop for the rest, I found that my traditional pencil style is the most liked and what I enjoy the most, so I just emulate and enhance it through the digital medium My references are also almost exclusively photos! I do study other people's art but only mentally, I don't copy others because I'm too lazy to practice through that way