Find test dates and make an appointment if necessary. Most who take the CAHSEE test are in high school, and the dates for the test are announced and tests are administered at the school. However, adults seeking a diploma in the state of California will also have to take the CAHSEE, and the California Department of Education advises that they contact the local high school district's adult education department to coordinate testing dates.
Access information on the tests. The California Department of Education (cde.ca.gov) offers released test questions and "blueprints" of the test to assist students in preparation. A blueprint outlines the various skills and knowledge that will be tested, and the percentage of the test that will be devoted to that particular skill or knowledge. Cliff's Notes (cliffnotes.com) publishes a study guide for the exam, as well.
Download a free study guide from the California Department of Education. These documents are also available in Spanish.
Take an online course. Some programs, such as those at testprepreview.com, are self-guided courses that you can do at your own pace. At xprep.com, you can have a free trial of the course to see if it's for you, and the cost is between $39 and $79 depending on the options you choose.
Work on your areas of weakness. The CAHSEE will focus on math and language arts, and it does contain a writing section. The San Diego County Office of Education has an excellent site with specific tutorials for every skill within each area (sdcoe.net/cahsee.asp) such as sections on prefixes, irony, and paraphrasing for language arts, and polynomials, graphing, and measuring in the math section.