For all games designers

From "Chris Avellone Blog" (Creative Director (and Lead Designer on our Alpha Protocol CIA RPG) here at Obsidian Entertainment.)

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ONE FINAL QUESTION. Do you have some tips and tricks to new game designers (people who already are one)? What "traps" they should avoid and what do you want them to focus on?

Document all you can in case you're hit by a bus but don't make them so exhaustive that no one ever reads them - keep it to bulletpoints, streamline it, use mock-ups, and if a particular design runs more than 3 pages, consider fragmenting it into its own document to ease reading. Details matter. Learn scripting, make attempts to understand the tools and pipelines of other departments. Don't just play other games to get ideas - read books, graphic novels, history, non-fiction, and expose yourself to a variety of media to round out your design ideas. Learn to recognize design clichés. Play with game tools and game editors across all genres. Resist the urge to re-design the wheel - if the wheel works well, just use it and then build new content on top of it (this especially applies to genre-specific interfaces). Prioritize your work and recognize that it's unlikely that everything you design will get into the game, so be considerate and manage your scope. Ask for critiques of your work frequently and often if you're not already getting it. The sooner you can play a design, the better, so learn to prototype (it doesn't matter what engine you do it in, if you do it in Flash, or whatever). This could go on forever, but that's the short of it.
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and

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b) Also, what makes a good character?

Consistent, believable motivation and a believable personal agenda. A tie to the game's theme either to reinforce it or as a sounding board for exploring a different perspective on the game theme. An emotional tie to the player (either hate, envy, love, friendship, respect) and reacts appropriately to the player character's actions. Proper casting of a voice actor or, if text only, insuring that the right writer is assigned to developing that character because they understand it (some narrative designers can't write sociopaths, do reverse gender romances, or commit to doing a goodie-two-shoes character). For a computer game, I feel it's also essential that the player understand the purpose of the character and that the character fulfills that role in the game mechanics and the world (for example, companions in F2 needed to be an asset in and out of combat, which I learned in Fallout 2 - Cassidy was much more valuable and appreciated than Myron).
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This man help to do Torment, Kotor2 and now it's working on Alpha Protocol: there something else to say?