Define the purpose for taking an aptitude test. Aptitude tests provide evaluations of different skills or personality types of the test taker -- in essence, how the test taker prefers to function in relationship to the world. Make notes on your conclusions.
Identify the available tests and the type of aptitudes each test measures. For example, a test taker who needs to take an aptitude test while still at the high school level or earlier will want to identify one or more tests that assess their likely abilities in a wide range of areas, such as physical dexterity as well as verbal and mathematical skills, because the combination of skills will suggest potential careers and the type of post-high school education or training to consider. Someone already in the work force who wants to advance in a current career -- or who wants to change their career -- should take a test that focuses on identifying their preferred work style and how that fits into work performance.
Establish the options within the type of aptitude test you have chosen. For example, someone who wants to identify a career direction after high school will want to consider a consolidated aptitude test, such as the Birkman Method. Those who want guidance pertaining to their work style and its effect on their career outlook will want to consider personality tests, such as the Myers-Briggs test. Add notes about the test category that best applies to your situation.
Determine the cost, if any, of taking the test and how that cost fits within your budget constraints. You can find tests that come as both a self-directed form or a form guided by a employment professional, such as a guidance counselor or a career development counselor. You can find self-guided tests online, as well as in career-related books.
Eliminate any tests that do not fit your purposes, based on a combination of factors you have identified. For example, if you want to get expert direction from a professional and need a comprehensive test -- such as the Birkman Method -- but you have no budget for hiring a vocational counselor, you can find an aptitude test administered at no cost through most state offices that administer career development and unemployment insurance programs.