To some this seems very elementary, but I see questions on shuffling posted quite frequently in my travels.
In my opinion, there is no right or wrong way to shuffle. I think the important thing is to be calm, keep your question in mind, and use whatever method you normally use to mix the deck.
Some readers feel Tarot cards should never be shuffled per se, but rather mixed by holding the deck in one hand and pulling cards from various parts of the deck and re-inserting them with the other over and over until you feel they are well mixed. Personally I shuffle them like a poker deck, 3three or more times. Why three? I don't know, it just seems like a good minimum. I usually shuffle 4-5 times, but never less than 3. If the deck is new, I shuffle at least 11 times.
I read somewhere that statistically speaking, it takes 11 shuffles to get a 78 card deck in random order. One day when I'm really bored, I'll do the math for myself and verify this. If you don't use reversals, you should be careful to keep the cards all in the same direction. This is difficult with some decks, because it is impossible to tell the direction from the back.
Getting a few cards reversed is not a tragedy, just flip them over. If you do like to use reversals, turn one pile of the deck over once or twice while shuffling.