Read, study and work with the cards
To be honest I still have plenty of moments where I'm confused about the meaning of a card--you're right, a person could only ever pick up two tarot decks/books in his or her entire life and become quite confused by the differences between them.
So learning tarot has to become a combination of what you read and what you intuit. For the first couple of years I remember thinking I wasn't getting anywhere with tarot study.
For some reason, one day it simply occurred to me that I knew a great deal more about tarot than I'd known the year before, so people do accumulate knowledge along the way, they just may not always realize it.
But learning tarot is and always will be an ongoing process, which is one of the great things about it. There's always a place to take it--if there weren't, it'd get pretty dull pretty quick.
Kalin