There are two possibilities for Math CSET: Foundational level subtests I Algebra and II Geometry for teaching those content areas as well as general math, probability and statistics, and consumer math; and Math CSET including subtest III, Calculus and History of Math, that authorizes teaching of all math courses.
Familiarize yourself thoroughly with the CSET test and practice questions at http://www.cset.nesinc.com/CS_SMR_opener.asp.
Print and study carefully the Mathematics Subject Matter Requirements and use them as your guide preparing for CSET. The theory on CSET is particularly tricky so spend time mastering all theories mentioned in the test descriptions.
The curriculum frameworks http://www.cde.ca.gov/ci/ma/cf/index.asp and content standards http://www.cde.ca.gov/be/st/ss/ are invaluable. The Glossary should receive particular scrutiny. This is the content you will need to master as a mathematics teacher.
This link is to the Math frameworks, 1999: www.cde.ca.gov/be/st/ss/index.asp
Look at the New York Regents Exam material online at http://regentsprep.org that includes study guides, strategies, and old exams for Math.
Utilize the free-of-charge online test preparation sites available at UCI's Open CourseWare website:
CSET Mathematics I: Algebra - http://ocw.uci.edu/courses/course.aspx?ID=25
CSET Mathematics II: Geometry, Probability, and Statistics - http://ocw.uci.edu/courses/course.aspx?ID=26
CSET Mathematics III: Trigonometry and Calculus - http://ocw.uci.edu/courses/course.aspx?ID=27
Make sure to read relevant sections of the CSET Tips page as it contains invaluable strategies to help you do well on test day.
Some books for CSET study available from the UCI Bookstore:
A first course in Abstract Algebra (by John B. Fraleigh) (chapters 1 & 5 [section 1])
Introduction to Probability Models (by Sheldon M. Ross) (chapters 1 and 2)
Complex Variables and Applications (by Brown & Churchill) (sections 1-9)
Elementary Analysis: The Theory of Calculus (by Kenneth A. Ross) (chapter 1)
It is essential to know how to solve the CSET sample questions that you can download from the CSET website. The books mentioned above will help you to understand and solve these sample questions. For Geometry, you should look for ways to prove theorems taught in high school (see frameworks above).
Students have recommended for Foundational level:
Schaum's Outline of Elementary Algebra, Barnett Rich
Schaum's Outline of College Algebra, Murray R Spiegel
Schaum's Outline of Geometry, Barnett Rich
Algebra to Go: A Mathematics Handbook by Andrew Kaplan (Editor)
Geometry to Go: Great Source Education Group.
Algebra, Geometry, Pre-Calculus, Trigonometry, and Calculus textbooks are available for check out from the Student Resource Center.
MacTutor History of Mathematics
An extensive and searchable arachive covering famous people and concepts, as well as describing the development of mathematics in various cultures: http://www-groups.dcs.st-and.ac.uk/~history/
Math Forum: Famous Problems in the History of Mathematics
History of mathematics presented through famous problems, with some exercises and their solutions.
The History of Mathematics
Collection of original papers of Berkeley, Hamilton, Riemann, Boole, Cantor, and Newton. Includes background and notes.
Preparation courses and materials are available from Orange County Department of Education: http://ite.ocde.us/test_prep.htm.
Review AP test preparation and your college course materials. Schools textbooks are useful, too.