Visit the University of Kentucky College of Education's website (education.uky.edu) and click on "Teacher Education" under the "Academics" drop-down menu. Click "Fifty States' Certification Requirements" on the left-hand menu. Select the state where you plan to test for certification, and click on its link.
Look for a tab that says "New/Prospective Educators" or something similar on the page that opens. Then look for a link that says "Exams," "Credential Testing," "Credential Preparation" or something similar, and click on it. For example, if you are testing in California, click the "Prospective Educators" tab, then click the "Examinations" tab.
Locate the test you intend to take and click the appropriate link, then locate a link or tab that says "Preparation," "Study Guides," "Sample Tests" or something similar. For example, click on "California Basic Educational Skills Test" and then the "Test Specifications" or "Practice Test" links on the left-hand menu.
Use the information you have found to prepare for the test. For example, study the subjects listed on the "Test Specifications" page, then take and retake the practice test until you feel comfortable with the material.