There's no ceremony you have to do. There's no incantation. The deck doesn't care if your hands are clean. The only thing that matters is that you sit down, shuffle, and ask a question.
If you've never read before, here is the smallest possible version of a first reading.
Get a deck. Any deck. The Rider-Waite-Smith is the most-taught, the easiest to find books about, and the cards are illustrated with full scenes instead of abstract pip art — which makes them easier to read by intuition when you're starting. You can pick one up at any bookstore for under $30, or from the shop.
Find a quiet five minutes. Door closed. Phone face down. Light a candle if you have one — not because you have to, but because the body knows what a candle means and it'll settle you down.
Shuffle the deck for as long as it takes you to forget you're shuffling. There's no rule about how. Hand over hand, riffle shuffle, lay them face-down and swirl them around like you're making a soup. When the shuffle stops feeling like an action and starts feeling like quiet, stop.
Ask one question, out loud or in your head. The question matters. Don't ask "what's going to happen?" — that's not a question, that's a fishing trip. Ask something you actually want to know. "What do I need to look at this week?" is a good first question. "What am I missing in this situation?" is another good one.
Cut the deck once. Take the top card off the top half. Turn it over.
Look at it. Don't read anything yet. Just look. What's the first feeling that moves in your body when the image appears? That's the reading already starting. Most of the rest is just translating that.
Then — only then — look up the card. Read the upright meaning. Read the reversed meaning if it landed reversed. Sit with both. The card will tell you which one fits. The body will tell you which one fits.
Write one sentence about what you got. Date it. Close the notebook. Done.
Do this five days in a row and you will know more than you knew before. That's the whole craft.