In my RPG philosophy, the most important thing is agency, so that the players'decisions matter. This requires three consequences: First, the outcome of pretty much any situation is open and to be determined by character actions, including failure and success. Second, to be able to make informed decisions, it is necessary for the GM to provide a plethora of useful information. And third, respecting the players' freedom of choice might mean that a significant part of the preparations are now futile, or that the PCs utterly fail, because they decided badly.

The "skill" I require my players to have, though, is commitment. I want players to identify strongly with their characters, I want them to care about the game's setting and I want them to contribute on a regular base or to invest some time and energy, both during the game sessions and between them.

Also, basic communication and social skills are mandatory in my groups. Unfortunately, common decency like resisting the lure of your phone for the three hours or so of game night, having a shower before coming to another person's place or either arriving reliably on time or give a notice beforehand, so you don't waste everybody's time is not as common as one might hope.