I’ve had a lot of occasion to learn this one from my end. I see the game and its immersion as the main end, and the mechanics as a necessary evil that either prevents us from long “Did not!” “Did too!” arguments about how an action resolved or (hopefully more rarely) protects us from the full caprice of a control-freak GM. (That, and all my books are PDFs, which was once useful but is now something of a barrier because my best reading time is on the trolley. Whether acquiring an ipad will fix this is uncertain.) So once I’ve established myself in a system, it takes a certain amount of work to get me to stir my stumps into a new one; in fact, there’s only one system that I’ve been the one to find for the first time and sell the group on rather than getting into it because it was perfect for a game that someone else exquisitely pitched to me. On this, I’m pretty sure I’m not alone.
So what does a person trying to spread whatever system they feel like running in to someone like me need to do?
Before even getting into the system itself, find reasons why the prospective player is going to want to be involved in this game. Maybe you’ve got an idea for a plot in a universe she’s fond of, but it only really works in the system you’re trying to run. Maybe most of her current games have folded, and your existing game in such and such a system is her best shot at her gaming fix. Perhaps (when dealing with someone experienced but not in that system) she needs a break from her game, and you’re willing to step in but it’s going to have to be this game. In short, the object of the game is to make sure that there’s something about it she wants enough to be willing to step out of her comfort zone.
Now, try to figure out what points of the system will best appeal to the player. Preferably, this is something that she’ll remember while she’s reading through the rules, as a constant reminder that there will be payoff (particularly useful for the reluctant and the extremely busy). This could be based on similarity, where the game has a similar strength to the one she’s already playing. Or it might solve a problem that she gripes about her preferred system’s inability to deal with. There might just be something that it does that she wants to see done, like a really flexible magic system or a way to model character growth that doesn’t seem too arbitrary, or that she hadn’t even realized an RPG could be designed to do. Its setting itself, if the setting is inextricably linked to the system rather than only there as an outgrowth of your trying to find something that would work, might be what it takes. In some systems, it’s even the presentation; the last time I was sold on a new game was when one of my friends introduced me to the Dresden Files RPG, and half of what succeeded for me wasn’t the magic system (perfect for my style once I understood it), or the setting: it was the comments in the margins.
Last, try to anticipate the problems that your prospective player is likely to have with the system, or even the game you’re planning. In some cases, this might be impediments to getting into the system, like a particularly complicated set of mechanics for an action the player is going to want to take, particularly high mortality rates, or an overly complicated chargen. Another might be clashes between the system and the personality, like something that’s built almost entirely around combat on a player who really doesn’t care much for those fighty bits or for whom the novelty of combat dissipates within a couple of battles. Sometimes, it’s even more of a contextual problem; one person’s completely outclassed by the others on overall system knowledge and isn’t comfortable with the idea, or needs a little hand-holding to find a character concept. This is normal; it’s part of the learning process. And since unlike an academic subject or getting one’s daily supply of nutrients, learning a new game is optional, making sure that the player is distracted from, or at least has help with, her greatest stumbling blocks becomes that much more important.
If you want the player in the game, it’s at least as important to ensure the player doesn’t lose interest in the game as to make sure the player knows all of the rules of the game. Ignorance can be worked around. Dislike is a deal-breaker.