It is easy to then forget to skip the answer blank on bubble sheets and get all the answers out of order. Color the bubble lightly the first time through the test. The second time through darken them in. Don't use mechanical pencils. Analyze the answers.
Many answers represent answers that are common mistakes easily made by students.
For example, on a math question the list of answers may include the product you would get if you worked the problem backwards. Do not look for a pattern to your answers. If you have no idea of the answer, go with your gut feeling. Your first instinct is usually correct in that case. Don't change an answer unless you have obvious proof of a mistake.