I've got another megapost percolating, but I saw something from Warren Ellis and had to quote it:
Sometimes it works like this. You can’t choose what part of a story comes to you first. Sometimes you think of a setting first. Sometimes an interesting plot progression drops into your head and you find yourself looking for somewhere to put it, instead. Sometimes it’s the title first, or a character name, or even a line of dialogue from nowhere that kickstarts the whole thing. There’s no hard and fast method, no laws about how this works. Every job is different.
Quite, quite true. You get inspiration where it shows up and you don't complain about it.