Learn how to inlet, everything on a gun is inlet: lock, sideplate, thimbles, barrel, it's all inlet into wood. Practise this, get a chunk of hardwood, inlet some pennies, odd sizes of steel or brass, take a piece of copper water pipe and flatten it out then cut some shapes out of it and inlet them. Learn how to use basic tools like chisels, scrapers, small planes. Lean how to modify a given shape, learn how to drive a chisel, use a file and rasp how to keep your tools sharp. Most of all learn how go work your hands and learn now to look. Depending on where you live, find somebody who does this and ask to watch as they build. Books are good, but they only take you so far, watching somebody is, in my opinion, the best way to learn this.
You will make mistakes, but that also is a learning process.