I usually do the setup, then play a mock game by myself as I read through the rules and if the rules are very unclear I will watch a how to video. I find I have a more thorough understanding of the game doing it this way rather than by reading straight through the rules first. I frequently teach games so, getting this sort of understanding, though more time consuming now, means less looking at the rules while teaching and a smoother experience for everyone.

I usually read the rulebook, then find a video (ideally “Watch It Played”, Rodney is a treasure) to confirm my understanding of what I read and/or clarify anything I didn’t. This is usually sufficient. Another cheeky way to learn a game is to play it on BoardGameArena where the system won’t allow you to play the game wrong.