Well, this is going to be a short one, I could end it with summing it up by saying.

PLAY IT.

BUT,
I am not going to do that too you. Yes,  you need to play a game it will be the best way to play a game for the first time. Through the game, you will learn how the game works. Yet there is still more than one way to play a game and learn it.

Look for Primers and Quick Play Guides.
These things will speed your learning curve up immensely. Game designers have set these guides up to get you into the game quickly and enjoying it all the while teaching you about the game.

Use a Pregen Characters your first few times. 
Pregens are not just for Con Games and one shot. Pregens if rolled up well are well by people who obviously know more about the game then you do. So you will gain a lot of inside from playing a Pregen for your first few games. With the added bonus of if you get it wasted, hopefully, you had not grown too attached.

Sit near the GM, or other players that know the system well.
Let’s just call this learning through osmosis. It also puts you in an area of the table to be able to get the most help the easiest and likely disturbs the table the least.

So there you have it. Did I miss anything ? Feel free to add any tips you have in the comments below !