Chris & Trish Meyer’s series of tips, tricks, gotchas, factoids, and shortcuts has continued with tips on masking in CMG Hidden Gems: Chapter 10 – All About Masking. If you don’t know already, check out the tip on hitting the Arrow keys while drawing Rounded Rect mask or Polygon/Star shapes.
For some handy info, see the sections on creating and working with masks in After Effects Help, and posts tagged mask at AE Portal.