Think of your favorite characters in fiction. Chances are, they behaved badly from time to time. Sherlock Holmes is excessive and frequently rude. Scarlet O'Hara is wily and audacious. Charlie Chaplin's Little Tramp is sweet, but subversive. Many of the characters loved in fiction have moments in their stories that would fit nicely onto the covers of tabloid newspapers.
We like our fictional characters to be outrageous. According to Jack Bickham, we need them to be outsized so we can see them through the dusty lens of language. In his book, Writing Novels That Sell, become talks about how he tried to make this point to his class by designing an absurd cowboy. He got plenty of laughs and, later, plenty of sales with that character in several books.
As much as writers enjoy outrageous characters, they often find them difficult to write. They are caged in by their own reasonableness. None of us wants to look silly. But we don't want to be boring, either.
In general, it is much easier to write an over-the-top character and tone him or her down than it is to take a more conventional character and add some zip. So, let me offer some suggestions.
Mine your childhood memories for characters. When we were kids, we experienced a lot of people via a big, ridiculous, and emotional view of the world. Over time, they may have become legendary to us. That makes them fair game for your stories. Give them a chance to live again in your head and in front of your readers.
Investigate heroes villains from history. Since history is written by the winners, there is a built-in level of exaggeration in the records. The losers are cast as more evil and the heroes are cast as more virtuous and stronger. It doesn't take much to grab someone like Hannibal, put him into your story, and discover what I guys you would march elephants over the Alps might do in a science fiction story or an action story or even a love story.
Read the Tabloids. Yes, they (and weird online sites) are out there. And they are as valuable to writers as they are to the Men in Black. It seems like Florida and Texas provide the best fodder for stories.
Would your characters do outrageous things? Try. See if you can make it work.
Minimally, list the most extreme things they would do. You can think in terms of story, but consider mundane things like how they eat, how they walk, what drives them crazy, what they are passionate about.
It's also a good idea to push them as far as you dare with one of the seven deadly sins.
For some reason, it's easier to give villains the best stuff. Give your hero an outrageous act you've assigned already to the villain.
Then think of the story goal. It must be pretty big to carry a whole novel. And life or death for your characters. What they would do to achieve their story goal? Consider all the outrageous stuff you've been exploring, and imagine them doing these things in service of the story, maybe even as a final test.
As an exercise, I force myself to come up with outrageous things respected people, like Nobel Peace Prize winners (well, some of them that are respectable), would never do, and then I imagine them doing these. It works often but not always. Some things, they would never do, unless...
And then I think of what the unless would be.
Free your characters.