Shuffling is an important step in the card reading process. It is the physical connection between the querent and the cards. However, this does not mean that there is any one "correct" or "best" way to do it. Whatever method is comfortable for you is best for you. You may want to choose a method that does not cause too much damage through things like bending or accidental folding.
When reading for yourself, you can shuffle the cards as many times or as thoroughly as feels right to you. When reading for someone else, shuffle the cards first, and then give to the querent to shuffle. This physical contact promotes a feeling of connection with the outcome of the reading.
Like almost all other aspects of the Tarot, shuffling is a matter of choice and preference. It is however important to approach the shuffling process with care: always respect your cards, and do not let them get damaged unnecessarily during the process.