When you bring home a new deck of tarot cards you want to clear them. Clearing is a process of spiritually cleaning the cards to remove any negative energy or blocks that they may have accumulated. When you clear a deck of tarot cards for the first time you are also putting your own energy into the deck. There are many ways one can clear a deck. It's a matter of preference for the reader.
It is suggested that when one gets a new deck of tarot cards that they are spiritually prepared and cleansed. This is so you can read more accurately. Negative energy and blocks obviously can impede the clarity of a reading. When you clear a tarot deck you are preparing them to use. In addition to clearing the tarot cards many readers also cleanse the space and objects they use in conducting readings also. The room you read in, the table you use and any other things related to the reader and the cards can be cleansed prior to a reading.
The idea is that a spiritually clean space along with the cards gives a clear reading free of the negative or blocking debris that collects naturally. This includes energy from other people and things like unwanted energy. The reason behind being spiritually cleanliness is that it is close to godliness or what ones perception of god is. Clean energy portends positivity. And you want positivity when you are doing a reading.
In addition to a initial clearings many readers do little cleanings in between their readings to keep their cards clean. This ensures that any negativity that was picked up in a consultation is dismissed and removed before the next reading. Some readers clean themselves and their cards after every reading and others choose to do it periodically. They may do it on a specific day and time on a regular basis. It doesn't matter how you clear your cards, all that matters is that you are calling good energy to assist you and removing any negative energy.
Like other forms of divination so are the Tarot cards. All types of divination require some sort of energy in order to conduct the reading. Clearing the cards and space eliminates the spiritual residue that the energy builds. This helps reduce the possibility of inaccurate and false readings clouded by that debris. This is especially true for those readers who let their clients touch the cards. When someone touches a readers cards; their cards are then picking up other peoples energy physically and psychically. In that case you don't want the next reading to have the last persons energy attached to it. Clearing your tarot deck and space is like giving them fresh air to breathe. You have to breathe fresh air yourself and so does the cards and your space to help you to give you the best reading you can give.