Sit down and write somewhere else in the story. Stuck in the middle? Write the end. Stuck at the climax? Rewrite the beginning.
If all else fails, write something else and then carry that momentum into your blocked story.
Creating deadlines for yourself is a good way to go if you’re method based e.g. “I have to have 5K words by X deadline so that so-and-so can give me feedback,”
Build a skeleton, fill out a character profile (likes, dislike, etc.), and then take a look around me or take a look at myself.
Maybe start out small. Try to make them a hypocrite about a tiny thing and then make them hypocritical about a big thing, then make that come back to bite them later.
I’ve mentioned this elsewhere, but make a Pinterest board! Get inside your character’s head and add quotes, sayings, nicknacks, and padiwacks to it. I’ve got a few and it’s a really fun way to explore your characters, what they might say, what they might do, and did I mention it’s just all-around fun?
Another tip - one that I haven’t had a chance to really explore just yet - is put your characters into AUs. If they’re based in an Urban Fantasy setting, briefly plop them into a futuristic Alien sci-fi setting and brainstorm how’d they react to that. Or maybe throw them back into the Wild West or toss them into a soul mate/bond setting. If you think, ‘well X probably wouldn’t like having a soul mate because Y’, then you’ve discovered a character trait and can use that in your main story about them.