Step 1: Get a cactus. Any cactus. They're all the same.

Step 2: Water it with tap water. Don't even think about it.

Step 3: Place in front of a window. Not too close, not too far.

DO NOT: Use a watering can. That's just a waste. Learn about the hidden dangers of over-watering Overwatering Syndrome: Symptoms and Treatment

And for the love of all that is holy, do not get attached.

Attachment Issues: A Guide