Go to the official civilian DSST website, Get College Credit, for the DSST exams.
Download the fact sheet for the Principles of Public Speaking exam.
Read over the fact sheet. As of 2010, the exam consists of two parts. Part 1 is a timed section of 84 multiple-choice questions, and Part 2 judges your ability to actually give a persuasive speech that is around four minutes long.
Use the "Content" section of the fact sheet to help guide your studying. This section discusses the types of topics that will be covered in the multiple choice section, as well as how best to approach the speech required in Part 2 of the exam.
Buy or borrow as many of the books or materials mentioned in the "Studying for the Examination" section of the fact sheet as possible. Current editions of Joseph A. DeVito's "The Elements of Public Speaking" and Stephen Lucas's "The Art of Public Speaking" are among several recommended. The listed materials are the ones most likely to give you the knowledge base you need to pass the exam easily.
Seek out feedback from people who have already taken and passed this exam, in order to know what to watch out for or what else to focus on. Forums for students seeking credit by exam, like the one at the website Degree Info, often have feedback from past test takers on this exam. Paid DSST preparation materials are also available from online retailers like Amazon.com, as well as the official website.
Practice giving impromptu persuasive speeches on a variety of topics to prepare for the test. Also practice with the multiple choice questions located in the fact sheet. According to the DSST exam website, there is no official practice test for the Principles of Public Speaking exam, so don't waste time looking for one.
Take your exam. Go through the questions carefully and record your speech. Then prepare to wait for your results and see if you passed. The speech recording must be scored separately, so it can take several weeks to get your results.