The more cards you draw, the more information you will get. However, interpreting tarot cards is often tricky, and thus it is wise to limit the number of cards drawn per reading.
Drawing 3 cards is standard practice and is usually enough to get to an informative reading. You can draw anywhere between 3 to 5 cards to get a good reading and make sure you don't get stuck. Once you get better and swift with your readings, you can progress into drawing more cards.