The question to ask you is probably what scale are you planning to sculpt in?
the two I use most are funnily the first on the list;
-\"Bill Horan\'s Military Modelling Masterclass\",
Bill Horan, Windrow & Greene Ltd., hardcover. This books is on sculpting military figures larger than 54mm. ISBN 1872004091 (1994).
\"Conversion and Scratch Building of Model Figures\",
Andrea Press, Paperback 40 pages, ISBN: 8493440442 (October 10, 2005)
Bill\'s book is just an inspiration start to finish, and although he does 54mm, the technique in principal is transferable to 28mm with the use of plastic torso from GW
The Andrea is quite thin, and a little flowery in translation from Spanish to English, but is a little gem. The scratchbuilding section I believe was written by Freeman from her, but may be wrong.
Using the technique from the Andrea book, I\'m well into a 65mm figure, who started off like this:
the armature is copper wire from Hobbycraft twisted together in a minidrill. All sealed with putty (Magic Sculp I\'m using)
The other thing worth getting at this stage is an anatomy book. I bought a chunky one at a discount book shop. Ming Hua\'s lists have a load there.
For wrinkles of clothing, take a photo of yourself!