I agree with all the above. Shep's book, "Building and Painting Scale Figures" (Kalmbach Books, ISBN 0-89024-069-8) is the bible and will give you basic techniques. It was recently reprinted, so it should be available from any dealer who sells figures.
I also have Mike Davidson's book: "Painting Miniature Military Figures," ISBN 0-88740-625-4. It and some of the others in the series should also be available from dealers.
Verlinden offers "The System - Vol 1" on figure painting. Available from Verlinden. Look at this one before you buy it. It has worked for others on this site, but I found the others above more helpful.
There are a number of articles on the subject in Historical Miniature Magazine ("HM") and back issues of Military Modeling ("MM"). If you have friends with back issues of these, ask to look through them for articles. There was a series in MM a few years ago for beginners that was quite good. Phil Kessling and other Grand Masters have done numerous technical articles on this subject over the years in HM and MM, which is why I would also highly recommend that you subscribe to a figure mag or two. Historical Minitarues is the best, IMHO, and Figures is also good - though not geared to oils. MM will have the occasional figure article, but it is geared more to armor and modeling. Look for it from dealers and buy it selectively.
Bob Knee's book is also good, as you will need grounding in color theory. There are others available, but Bob's is geared to figure painters like us. I also highly recommend that you go to book stores and search our other books on fine arts oil painting, composition and color theory. Also look for books on the masters such as Rembrandt, who is a master of portraits. We are not in a vacuum here, and many of these techniques can be applied to figure painting. These will also give you insights into the use and characteristics of oil paints. One book I like is "The Big Book of Oil Painting" by Jose Parramon, ISBN 0-8230-0498-8.
When I was learning, there were a few things - like applying and blending and the consistency of the oil paint - I could not get from a book. I learned these because a dealer/oil painter took time with me to show me what he does. SO, nothing replaces watching someone or asking for advice at shows or club meetings.
Good luck and Happy Painting.