Usually when I'm set out to write a module or adventure for a roleplaying game I usually start with the question "What game do I want to play?" and then I go from there, trying to write an adventure for a particular game.
I am more and more starting to think that that's a slightly flawed concept. (At least partially. For a long-running campaign, you are usually bound by what game is played in the campaign. )
So, what's the alternative? Perhaps, the question shouldn't be what game to play, but rather what I want to simulate/ "experience". From there, I can pick an appropriate game rather than the other way around.
Of course, there are situations where you want to pick a specific game (it has a new concept or interesting rules to try out), but overall at least my tendency is to think game first and "situation/story" later. I will try to change this, and first and foremost think about imagery, stories and scenes.