And of course, there is the theory that it is all shysterism, the reader just says what they think the querent wants to hear. Study the cards and learn their meanings. Practice a lot, on yourself, friends, or total strangers as suits your personal leanings. Eventually, you should get pretty good. Some people prefer to learn the cards intuitively, by studying the illustrations, meditating on them, and carefully recording their reactions to them.
Most people just read the little booklet that inevitably comes with the deck.
The most common 'spread' for Tarot readings is called the 'Celtic Cross'. Represents where the querent is at the time of the reading. Lies across 1. and represents what holds the querent where they are. Represents the 'base of the question' - why it is being asked. Represents how the querent has been thinking about the question.