Well, I am all for quick answers (yes, I know I never give them) but there were two words that leaped straight to my brain when I was asked what the best way to learn a new system was. Run it.
I do not play all that often in the PC seat. I always tend to be the GM and hence I always, ALWAYS, read a new game from the point of view of how I would run it. In fact, much of my interest in games comes from challenging myself as a GM. I run a lot of safe games like Pathfinder (not to say that is not a daunting system to a newcomer) but the ones that I get the most reward from are the ones that ask me to challenge my notions of being the games master. Lords of Gossamer and Shadow, Apocalypse World, FATE, Cypher – these are the games that I feel rewarded for running.
I apologize that this answer is not a great help for the players out there, but if you want some advice…
Know your character
Honestly, this is the best way to know your new system. Find out what your character can do and be well informed on it. Much of my time as a GM in games like Pathfinder is taken up reading spells and rules of player characters because they do not know them at all. They just see a pretty title and say they will do that, no thought or pretense in between rounds. Do not be this person. This person is the hardest person for a GM to deal with because they are lazy. It is OK if you are completely new to RPG’s but if you have been playing a while, get a copy of the rules you need and read them. Know your character. Go on – it is rewarding!
So there you have it! A couple of great bits of advice around this very simple question! Keep rolling!