Mostly by trial and error. I've been self-taught since I was 19 and learned by exploring the program to create awesome visual effects. I literally clicked on every single menu, checkbox, or icon you could click on to figure out what it did. I started with Photoshop way before there was a YouTube, or even a Facebook (actually there was not even a MySpace!). At that time there were not as many resources as there are now, not many videos or websites where you could learn, especially for free. But I did manage to find a handful of websites that helped me a lot. One of the big reasons why the Photoshop Training Channel exists is to save people from the headache and the thousands of hours I had to spend learning how to do what I do. However I did buy a training course that was about 12 hours on CD Roms, and I watched it twice! That helped a lot.