-A player who understands the job they're playing. They don't need to be perfect, but they should know basic things like how/when to AoE and the bare bones of their single target rotation.
-A player who understands the fight or is quick to pick up and adapt if they are not.
-A player who uses their support abilities (Goad, MP shift, Diversion, Foe's, ect).
-A player who is friendly (chatty if the party is chatty or even just saying hello and thanks for the run).
-A player who tries to defuse drama if it occurs rather than make it worse or staying silent.
-A player who is willing to admit when they made a mistake, apologize, and correct it.
-A player who is willing to learn (ask questions, take advice, try something different).
-A player who goes out of their way to help make things easier (those healers who pick up keys, open doors, go down side trails to get chests. Love those guys).
-A player who speaks up if they're new/doesn't lie about not being new (I guess this is mostly a PF thing).

You don't need to be a raider. You don't need to be perfect. Basically as long as you're not a PoS, are willing to learn, and help others, then you're a good player.