My process used to be:

1. Read the rules before everyone arrives
2. Play the game and have fun
3. Read the rules again
4. Email everyone with everything we played wrong

Now that I have kids I don’t always have the luxury of reading the rules the same day we play the game, so what I usually do is I read the rules a few days in advance, which means I won’t remember as much when the time comes to play, so then I end up complementing that with a rules explanation video.

I read the manual and then I search the internet for any rule unclarity to se if there is an answer (errata, FAQ, community consensus). Almost never watch videos, don’t learn from them as well as I do from reading. Usually read the rules if I’m going to introduce someone new to the game even if someone previously explained it live. Have had to many cases of someone teaching the rules wrong, to blindly trust someone (except like one other person I know who is usually correct about everything)

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.

Play it on yucata.de with a friend.

Then take a first look at the rules halfway through the game to try and figure out win conditions and play mechanics.

Also viewing Watch it Played, SUSD or random HOWTO videos.

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 watch a video after reading the rules and trying to play for a little bit. It usually helps cover the gaps in understanding or areas that I’ve misinterpreted the rules, while also allowing myself to become familiar enough with the game that I don’t get lost.

I’m usually the one teaching new games, so I have to learn them thoroughly beforehand. I do all of the above. I will watch a video first to get a good idea of the flow of the game. I really like Watch It Played. He does a great job of explaining the rules without being to wordy and in the weeds. Then I will read the manual and play things out so I can really see how things work. This way I can get all specific rules that may be glossed over in the video.