There is no single book for writing test cases. Writing test cases is an art which you acquire over the time by knowing various facts/methods/types of testing. Go through testing types and start preparing cases for your application according to type.
A highly advanced bug is indistinguishable from a feature.
1. Effective Software Testing by Elfriede Dustin
2. Rapid Testing by Robert Culbertson
3. Quality Web Systems by Elfriede Dustin (if applicable, don't know what your AUT is)
4. Testing Web Applications by Hung Ngyuen (if applicable, don't know what your AUT is)
And do some Advanced searches here using: Test Cases, Test Requirements, Test Design, etc. as your keywords...