Tools are the single most important part for sculpting your oil based clay characters. And guess what the magical, most widely used, best tool there is for sculpting? Your fingers of course.
Your fingers can squish, smooth, pinch, flatten, and poke clay better then any tool. Good metal, plastic, and wooden tools are important as well. These kinds of tools are used in places where detail is too small for fingers to get into or for sharp clean edges.
Sculpting tools also scoop out holes for eye sockets, and ears, and mouths.
One tool that you wouldn't think of for sculpting oil based clay is the paintbrush, in combination with a 35mm film can. John Ashlee taught me one day when I went to visit his studio, how you take a film can, stuff a wadded up paper towel inside of it, and pour mineral oil "we now recommend olive oil" inside of it until it is absorbed by the paper towel.
You keep pouring, until the paper is saturated enough to where you can take your finger and rub the paper towel with your finger tip, and get a nice thin coating of oil on it. Then in the future you can just dip your finger in it, and use your oily finger to smooth out your sculptures. You also use the soft but firm bristled paint brush to get onto fine detailed areas using the same process.