Make sure you know understand the format of the quiz. Is the quiz for credit? Are you allowed to take it multiple times? Is it timed? Will you need a password? If you don't know the answer to any of these, ask your instructor.
If the quiz includes essay questions, it may be advantageous to use a word processor to type responses, and then cut and paste those responses into the answer text box for the question. This will allow you to make use of a spellchecker. It will also allow you to save your work in case your Internet connection fails during the quiz.
Refrain from using the Backspace key when working on a quiz. The Backspace key can act as the Back button in a browser; pressing it may take you back to a previous Web page. This would delete any work done in the quiz and may lock you out of the quiz.