Step 1 - Read The Original Post- Meaning read the first post of the thread, this post usually states the rules and who is in charge of the questions.
Step 2 - Read the last question- The only question one should answer is the very last one asked. Answering questions three pages back is not the proper way of doing things.
Step 3 - Answer the question- If you happen to know the answer or you have a good guess, go ahead and post.
Step 4 - Rinse and repeat - If there is one person asking the questions on the thread, wait for their response. They'll usually state the right answer and if score is being kept, they'll tally up who earned a point. Some threads may work differently, for example, every poster answers and then asks a different question, etc. This is why its important to read the original post.
Other guidelines to follow-
Obey the "host" of the quiz (the person asking the questions)
Don't Post more than once in a row
Don't start another quiz thread if there is already an active one on the board.