What I usually do when I go on a trip to photograph a specific species, is a lot of research on what kind of pictures have already been taken of it. I use (photo) books but also the internet to see what's been done already and if there is anything that I can come up with to create something different.
For one of my first trips to Japan I looked at thousands of images of snow monkeys for instance and noticed that most of them were done with on-camera flash, mostly to brighten the face and the eyes and to compensate for the low light levels. During my visit I used flash as well, but I decided to choose a different approach. Instead of keeping the flash on the camera, I positioned it at a distance and to the side of the subject (with a radio controlled remote) to create more three dimensional side-lighting. I underexposed the ambient light for extra mood and to emphasize the lighting, and eventually came up with this shot.