The short answer is by playing.
Especially for tabletop RPGs there’s little you can do other than playing in order to learn. Of course, reading the rules helps, but without applying them by playing you can’t really grasp them.
I had played D&D only once before I started DMing and that game was in a different edition than the one I wanted to learn. So what I did was read the rules and create a character. It took me a couple of hours and some Internet searching but in the end I made it. And after that I ran a game. It wasn’t easy but I survived.
The same goes for Android: Netrunner. We started playing while also reading the rules about a week ago. And now I believe we’re actually good at it!
So my advice is:
There are a couple more things you can do but I consider them a bonus.
Join an experienced group. If you can do that it will help you a lot. The other players can help you and you can also watch how a DM in their natural habitat.
Watch other people play. That’s more helpful for tabletop games(not RPG). For example, watching videos of others playing Settlers of Catan helped me a lot.
And that’s my answer to today’s question. I believe, up until now, this the question I enjoyed writing about the most. Let’s see if that will change until the end of the month. Tomorrow’s question is: “What is the most challenging but rewarding system have you learned?”.
So until then, have fun!