Guess I could throw in my two cents. [b]*Speaking from the perspective of a GM*[/b]

... Biggest thing that comes to mind is tone. A GM is a person who runs a world, NPC's, and plot. While they wield power, their role is not to antagonize or attack their players. Their role is to use their power to provide entertainment for the players and themselves, maybe by providing a challenge, maybe by weaving a story, etc. Compromising on minor points helps, be humble, and be inclusive: Actively plan with players, if you say no to something (like an item or power) see if there isn't a way to weaken it instead of outright throwing it away, or making it something to be earned as part of the journey. Actively try to incorporate the player character's history, look for tie-ins... A significant way you can convey this is with the tone of your writing.

There's a significant difference between the following two statements, for example.

"You're wrong, this is my RP, and your character is rejected." Versus... "I like your sheet! Though this one part here could be touched up, here's a couple suggestions. Thanks for your interest!"

The first sentence is aggressive and authoritative. The second sentence is positive, complimentary, cooperative, and constructive.

[i]Seriously do this. This alone probably doubled my player count.[/i] It also makes players feel welcome, which is what you should be aiming for in a successful RP.

As for players, make requests, not demands. You are not entitled to jack shit in another person's RP. You're not even entitled to being there, you could be kicked out or your character rejected. Treat the GM with the same respect you expect to be treated with: If you want the GM to be informative, return that kindness. If you want your GM to be active, you should also be active.

Ideally, there shouldn't even be an "us versus him" mentality between the players and the GM. You could even compare it to a job if you want: The players are employees, their characters are their resumes and acts on the job, and the GM is the one assigning tasks and managing their department. Sure, everyone can fight and be distrustful and make demands and go nowhere, or everyone can work together, be cooperative, learn how to talk like a decent human being, make requests instead of demands, compromise...

tl;dr: [b]Be a decent human being regardless of whether you are in power or feel offended[/b]. Everything else tends to fall in line after that.