Having a good, solid, working knowledge of wood types, moisture content, sound qualities, how to work with them (some are more prone to splintering than others, like wenge) and good, solid, working knowledge of wood working skill and techniques are needed. Being able to make good, straight, clean cuts and joints, etc.
There is a difference in the woods used for stringed instruments vs. making furniture, although all of the wood working skills are much the same.
Other than the scarf joint and dovetail work for set in necks, there really isn't (I'm gonna catch heck, here..) any complicated jointery, but solid, straight joints and glue lines are needed.
You will also need a solid understanding of the different finishes and techniques used, and if making electric instruments then good soldering techniques, and an understanding of basic electronics (Ohms law, etc.).
All of this can be learned on your own, from reading books, hanging out in forums like this one, reading other luthier sites that have great information about woods and techniques (like the Warmoth site or Ken Smith's site....), or sites dedicated to Lutherie like
www.luth.org, etc.
There are schools dedicated to teaching lutherie, and the luth.org site lists many of them.
There is a TON of info available to you to teach yourself, and if you don't have any wood working experience, I would check with some local community colleges for some adult education classes on basic wood working.
Lastly and most importantly, I firmly believe that you need a PASSION for wood working and making instruments. Don't do it just because you think you can make a bunch of money at it. Yes, you can make a decent living at it, but do what you love and the money will follow. You have to love the work.
:^)~
