I keep a sketchbook of quick renderings when ideas come to me. I also keep a file of ideas from images on the internet. Not everything turns into a carving, but I never run out of ideas!
Most of the time, I develop a pattern from a rough sketch and start carving. More recently, I have also been sculpting with polymer clay to have a 3-D figure as a reference when I start the carving.
The last stage is to carve and paint the piece. The finished piece seldom is exactly the same as the rough sketch and/or sculpture since I like to make further modifications to the design on the as I go.