I'm assuming you mean for fiction:Things I do:
Make lists. Lists of titles, character attributes, anything you might want to add to spice up a story. Then write about one. A lot of my best ideas started with a title. "The Vampire's Lament." "Blessed Event." "Days of Rage." "A Simple Twist of Fate."
Carry a notebook EVERYWHERE and write down every creative thought that occurs to you, even if you think it's silly at the time.
Rewrite TV show episodes in your head, with the same situations but starring character/s of your own invention. You can also make up story-videos in your head to songs, also starring your characters. The plot idea for "Blessed Event" (mentioned above) came to me while I was listening to that sappy "All I wanna do is make love to you" song.
Schedule a little time to go mad. Not dangerous mad, just "a bit off" mad. The best poem I ever wrote I wrote at 2 AM after a megadose of sugary iced tea and a mile-long walk in the dark to a friend who wasn't home's trailer, while muttering to myself about alternate dimensions and magic and casting seven shadows at once.
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"Nobody knows this, but I'm scared all the time... of what I might do, if I ever let go." -- Michael Garibaldi