First thing to do is to know your goal, to have something to model it after. This site had amazing examples, so i used it http://www.gwbasses.com/gallery/index.shtml After that, mark out the rough size in pencil, don't forget depth. As you can see, this variety of arm contour can get pretty deep into the body, so i like to start small, then check it, and re-plan for more depth, until it is to your liking. I had to be careful on planing my location, since the bass was a hollow-body. Hand tools used where a small wood gouge, flush cut saw, chisels, and sandpaper.