Comments on a recent post got me thinking: most people who talk about RPGs online are DMs - content creators, organisers, systematisers. People who are only ever players are a kind of silent majority. This means you don't get much discussion regarding how to be a good player, or play theory, or whatever. Or you may see the occasional list of desirable traits without much elaboration on how you get them.
What makes a good player? Lateral thinking is extremely useful, as a means of traditional problem-solving but also simply as a way to be creative in reacting to what the DM throws at you. (Not that I want to turn into Edward de Bono all of a sudden - I've always thought he was kind of a knob.) There are all sorts of techniques for getting better at this, of course - not least the book Lateral Thinking itself. This is the kind of skill that results in players planning to assassinate a powerful nobleman they've discovered they have to kill by putting explosive materials in his horse; using the corpses of enemies as a sled to slide down a rapidly collapsing pyramid; or relocating a river mussel goddess to a human settlement so she can live off their detritus as a means of persuading her not to kill people anymore - all of which are examples that spring to mind of things that have happened in games where the lateral thinking of the players has impressed or surprised me.
The importance of paying attention goes without saying, but it's all well and good saying it. How does once get better at it? The obvious thing is making notes - important names, importance places, important rumours. Jot them all down somewhere so you can refer back. So that you don't forget entirely or annoy the DM by constantly asking "What was that guy's name again? You know, the guy with the stuff."
A third thing: think about consequences and air them. A creative DM has to have ideas to riff off. This may be a view behind the curtain that reveals a bungling technician where there ought to be a wizard, but I'm sure I'm not the only DM who steals ideas from the players when they are idly ruminating and then runs with them. Players' fears, hopes, dreams and anxieties are part of the stuff of the game - part of the glorious feedback mechanisms that make a campaign sing. So to be a good player, speak a lot about what is going on in the game. Ruminate on things. Give him stuff to work with. A good DM won't just use what you are thinking directly. But he will pick it up and twist it, stretch it and spin it around to make the game richer and deeper.
Is that it? It'll do for starters.