We've all met boring people. Some might even say I'm boring, if they were unfortunate enough to meet me on a zombie-like day, which are fewer and farther between now that my sleep schedule is returning to normal. (I've heard that happens as children age.)
But I digress. Boring people exist. They are characters with character merely by the fact that they are so boring, whether by droning on and on in monotone about how the fungus Gliocladium roseum produces hydrocarbons--not necessarily boring to those interested--or sitting in stoic silence while everyone else laughs uproariously at the funniest joke on earth--or course, that might just make the bore a boarish.
However, no one wants to read a book about a bore, or at least not one where the bore is the only character in the book, but I still bet the reader would remember the character if the writer were consistent enough in making him, or her, a bore.
Consistency is key in making characters with character. Even the mercurial character must consistently, though hopefully only in the most unpredictable ways, maintain the role by doing the unexpected or responding with an unlooked for biting or supremely witty response.
But how does one write a character with character?
Personally--assuming somewhere along the way I've managed to actually learn how do this--I've found it is impossible to do this in the first draft. The first draft captures the essence of the plot, provides a rough sketch of the character. It's the polish that brings out the shine though. Like an artist painting, pass after pass illuminates certain aspects of the characters, draws the reader's eyes to main features.
So, don't look at writing as a race to the finish. Don't think the first draft is the piece de resistance. Instead, take your time. Set the first pass aside for a day, a week, a month, whatever it takes to gain some perspective then layer on a second coat. Repeat until your work shines.