Locate and contact a licensed psychologist who performs IQ tests using the link provided in the "Resources" section of this article. The state psychological associations listed on the page can inform and refer you to a fully-trained professional.
Go to the Mensa Workout page listed in the "Resources". The tests provided on that page will give you an idea of how IQ tests work and what kind of questions you will have to answer.
Sleep well on the day before your test, and take a light meal before it. This will allow you to participate in the test in a relaxed state of mind, which might slightly improve your results.
Read the questions carefully during the test. Also, remember that IQ tests are timed. Therefore, if you experience difficulties with a particular section of the test, just skip to the next part. If you have time later, you can always go back to the difficult section.
Discuss the results with the psychologist. He will help you understand your score and what it means. He may also give you advice on how to test other parts of your personality in order for you to get a broader view of your personality and performance level.