On the whole, I've found that bad, or at least flawed, fiction is the ideal source. Good fiction, you can see the idea in action just by re-reading it. Bad fiction, the only way you can see the idea hopping through flaming hoops with more grace than a tiger is to make it do so yourself.
(Well, usually. Sometimes a throw-away idea is used as background, or a lie, or something, in good fiction and you can steal it and bring it to the foreground and so have a story.)
But not always. I was reflecting on Andre Norton's Forerunner Foray. There are two major things I noticed reading it as an adult that I missed as an adolescent. One was that the heroine and hero traipsed around in history without the slightest concern about whether they were affecting the future, or the well-being of the aliens and their civilization -- and given their status, they threw a real monkey wrench in there. And I played around with that and have a story about lords and loyalty and death. Also, the heroine's big motive was to Get Her Hands on an Alien Artifact. It obsesses her. Her boss thinks it's good treasure, another psyker thinks it's a valuable artifact. . . and no one thinks maybe this demonstrably powerful thing has an agenda of its own. Which idea sits on its own and does not sprout a story. . . .