Separate PCB ground planes for Digital and Analog (why ADCs in micros don't work well). A good book on such issues is:

The Circuit Designer's Companion
by Tim Williams
Published by Butterworth-Heinermann, Oxford
ISBN 0 7506 1756 X

While I'm recommending books here another good one for SMT board design:

SMT Soldering Handbook (2nd Edition)
by Rudolf Strauss
Published by Butterworth-Heinermann, Oxford
ISBN 0 7506 1862 0

Both books were sold through a book company named Newnes that sold the books through a store in the U.S. named Fry's Electronics. Both are from England but I found them easily applicable to the U.S. standards. My only recollection of its origin being noticable was a section wherein they price different capacitor technologies in unit British money.

aka j