The most sensible use of these quizzes is as a check on whether your understanding the material well. I therefore recommend that you always first read the material that relevant, and also that you try the written exercises (where those are available). It is also often useful to review the overhead sheets used in the lecture. Then try the quizzes in order to identify points in your understanding that are still vague or even wrong.
The effect is then optimal.
If, on the other hand, you begin with the quizzes, looking up just enough to get the answers, you run the risk of understanding only what's in the quizzes -- and not even all of that as well as you might.