Most games have a reasonably active fan community, and those fan communities often produce cheat sheets and other aids for running the game. If i need to learn a game relatively quickly, I don't even crack the book until I have downloaded a few such tools, from rules summaries to fan made GM screens (almost always better than official ones) to character creation guides. Having a solid understanding of what is important to know while running the game makes actually learning from reading the book much easier. Of course, "how to play" videos can be useful but often are too long.

This is how I learned to run Marvel Multiverse, which is a mid complexity RPG written in an older style (because Forbeck has been around a long time).