I think inspiration hits when I'm relaxed, not really 'trying'. For example, I came up with some concepts and plots during bus/metro rides; crammed into public transport with fellow commuters like a sardine, losing oneself in imagination seems a reasonable way to escape.
I think it's easy to come up with bad or boring ideas; it's pretty simple to take an existing concept (or genre) and rework it slightly, plugging in generic characters and situations. I find it difficult to settle on ideas that just feel right and 'original' (which, considering how absolutely everything has 'been done', is nearly impossible).
Recently, my Mom and I with my two daughters went out for breakfast. We were all discussing her new car, and started teasing her about her fast driving. I blurted jokingly how it'd be a funny story to have a Grandma driving wildly with a cute child through the city; as I mulled it over, an unrelated germ of an idea I'd had long before (about an oblivious elderly man facing Zombies) floated to the surface of my thoughts.
I could nearly hear a bell chime as a fun concept was born, one that I instantly found appealling and tremendous fun: a Grandmother and granddaughter drive through a post-apocalyptic world, fighting mutants. I whipped up some quick sketches, and couldn't stop grinning:
Of course, Thelma and Louise meets Mad Max isn't high literature; that being said, the idea screams 'fun' for me, and I think it'll be easy to come up with adventures for my daring duo. I mentioned it briefly on my Facebook, and folk seemed to like it as well.
I hope this glimpse into my creative process (which is basically random musings colliding in my brain) has been enlightening!