Ive been playing poker for quite a while. Thanks to my uncle Mark who is a insanely lucky gamble the passion has kind of built in me.
When I was in college I played play money all the time on line, before the big crack down on online gambling. I started out small at home games and small tournaments at the college I went to (CSUS go hornets!) and very slowly over about 3 years build a 2500 bank roll.
The bank roll I had built was blown in 1 weekend in Vegas. This is what I would say is a likely and common story. I was trying to be a pro poker player at this time tho, I was just messing around. While I was in Vegas with my uncle for my 21st birthday a met a guy, who I can see now, was an obvious pro. He told me to look up read and study a  book called Doyle Brunson's Super System. When I went back to school after spring break and my birthday in Vegas I had never really study poker. I didn't know about odd and poker math, and reading the board, all the money I had ever won was basically on luck.
My buddy Joe had won a little money online and he had the book. I read through it a little. I was already studying many courses in college and on a quest to get some tail so studying poker at this time wasn't a high priority.
Eventually I moved to San Francisco where I played here an there over the next year at Artichoke Joe's casino where I lost only a little money and never really came out a winner.
I was playing more regularly now usually with my Uncle Mark by my side. I would loss little at a time with very few wins. Uncle Mark would always tell me "tighten up" and I didn't really know what that meant at the time. I was out of college for a year and for my 22nd birthday my girlfriend at the time, who I am still on again off again with, bought me the Doyle Brunson's Super System. I started reading through the long read. It really was amazing how much there was to know about poker. I mostly read it on the john but i eventually got through it. I learned that i needed to play tight and aggressive. I learned to be patient because its job and money. Doyle told me story's of his experience and he said "there are no friends at the poker table" I took all these lessons to hear.
Basically immediate my game changed. I understood why you don't play 7 2 off suit and why suited connectors are important; and finally what playing tight meant.