I also have some thoughts on ‘system fluency’ in the context my friend, the Shadow Run GM, used the term. See, roughly two years ago my IRL gaming group reformed after a post-college break of multiple years. The GM hasn't had a chance to fully use the fourth edition of Shadow Run and wanted to run a campaign before he even considered buying fifth edition. Shadow Run is his system the way some folks apt D&D or Pathfinder reasons as their system: he knows the system lore and plot at a pretty deep level and it's his default system to run a campaign in. That's the kind of story he wants to tell (and yes, only tell — I don't think he'll be convinced to play anytime soon, if ever).
We have, on occasion, gone three months between sessions. Just life stuff killing scheduled time.
Ignore the difficulty of keeping a story going and fresh with such big breaks between events. We're having a hard time keeping the rules in our heads. The same things cause us to stop and look specific, fiddly rules up from session to session, players and GM alike. We aren't gaining system fluency. Our 'speech' in the language of Shadow Run is still halting and dependent on dictionaries/grammars. The rules and our lack of fluency in them is placing a barrier between us and the story we're failing to craft.
I honestly think system fluency (or lack there of) can play a big part in how enjoyable an RPG system or campaign is. How often have we heard 'the rules got in the way of the game'? Time spent looking up rules is at the table is time not spent interacting with friends or the story. Unless your type of fun is studying RPGs to gain system mastery, that's not fun. (And if that is your type of fun, you can do that in between sessions, yes?)
All of which got me thinking about system design and how the system can aid or hinder gaining system fluency. And how I can pick up new systems faster. Especially since I've been playing a variety of systems with Technical Difficulties.
Rules light, narrative systems seem, to me, like they should be the easiest to pick up. There aren't a lot of rules to remember and what there are should be core mechanics. Things that apply across a spectrum of situations. For example, in Monster Hearts, everyone had four basic moves; the trick was figuring out how you wanted to apply them to this situation and what they said about your character. The difficulty with narrative systems though can be the lack of rules. If the system doesn't do a good enough job conveying the expectations of the system, the type of story it's supporting, I at least can end up flailing, feeling like there's no direction to go and unclear even on what tone to take.
Take, for example, Fate Core and Monster Hearts — Fate Core seems like an awesome system, one I could see using for a sword-and-sorcery epic fantasy and for a gritty investigation. So unless the GM has a clear vision of the world they want to build, the genre of the game to play, conveys that to the players, and gets buy-in from everybody, I'd be flailing as a player. This is not to say I don't like Fate Core — I do, have read up on the system for it's own sake, and would be willing to play in a campaign (or one shot) of Fate or its derived settings (which I haven't read up on yet). But only with a GM who has a clear idea on a campaign. It's a broadly applicable narrative system.
Meanwhile, Monster Hearts has one story it's designed to tell: teens/young adults growing up. You can layer all sorts of stories in that, but that is the core story the system is built for. I've got a direction to take my character and a tone expectation built in. So the system is doing the tone and expectation setting, before the GM ever needs to communicate with players. Gods help you if you want to do a different type of game or campaign with the system though.
In terms of learning these types of systems, I try to focus on core mechanics and narrative feel. So I pay more attention to included fiction and rules examples.
On the other end of the spectrum are crunchy systems, things like Shadow Run and Eclipse Phase. My main attraction to Shadow Run used to be the cyberpunk setting, but over time the density of the rules and different systems for different classes (the magic system is different than the hacking system is different than the drones is different than...) has eroded my desire to play in the world. One of the things I think Eclipse Phase learned from Shadow Run is to keep the system flat. The magic system in Eclipse Phase is, fundamentally, the same system as performing any other skill: percentile dice under a skill rating target number.
Another thing the EP team is doing differently from SR is that the metaplot is not advancing — whether or not this is a good thing is more individual choice, but personally I'm in favor (and will get to why in a bit). In Shadow Run, there was a story line that canonically happened, lots of which were available to players as modules or campaigns, and then the world changed. It was time for the timeline in system to advance by five years and the next edition of the system to come out. Eclipse Phase is keeping the 'official' clock at AF 10 and diving deeper into various aspects of the setting — what would be the Monster Manual in D&D just came out (it's called X-Risks).
Both the crunchy systems I know are heavy on rules and setting (Shadow Run more on the rules, Eclipse Phase more on the setting). Shadow Run feels like it has just the one story to tell: go do an adventure from the perspective of people outside the power structure of the world. My GM has played at least one adventure of Lurg, the combat medic mercenary, but the campaign we've been trying to do as a corporate black ops team is the one that's not working so well. And the GM has quietly been doing a lot of work in the background to keep the system balanced (not that he really has that time to spend). Eclipse Phase, I've run a dungeon crawl, I can see a long political intrigue campaign, I've heard an actual play adventure quest, I wanted a different actual play campaign to stop play the war scenario they touched briefly, I could see running an investigation campaign. Heck, I could see running a police procedural. What I'm trying to say is that, like narrative systems, crunchy systems can range in scope of stories they support playing. So, you know, I think that's the place to start — figure out what type of story the designers expected folks to play in the system and use that to direct you to the rules to learn first. But for me, once I get the first set of rules, I really need to try an adventure or two. One, to figure out if things move fast enough that I want to keep playing and two, to figure out what set of rules to focus on learning next. Setting wise, I limit my dives into the sourcebooks to the areas most relevant to whatever we're playing next.
You know, if I don't have time to read them for fun.