I keep training myself to look at writing characters like how a small child would color.
Too often, if there's someone who partially inspires a character, I find myself unconsciously trying to paint that character within the solid black lines of what that real person is like. Then I become frustrated. Doing something creative, like writing a character, needs to be an action unfettered by limits. I want to take my pastels or charcoals and scribble wild circles of color and dust. But every time I start doing that, I start getting these niggling little thoughts at the back of my head ("He wouldn't say that!" "She hasn't done that!" "He'd never say it that way!") that make me stop scribbling for a moment...and consequently lose the moment.
It's difficult, but necessary, to distinguish personal inspiration from the actual fictional character that it inspires. It's vital to constantly remind yourself that yes, this is what the real person is like, but that doesn't mean your character must be like that, too. Your character can be whoever you want him to be, whoever you paint him as--and you sure as hell don't want a carbon copy of an actual living, breathing person, do you? The point of creating a character is to breathe life into him, to see his cheeks flush up with blood with every sentence he speaks, to see his eyes widen and narrow when he engages in action with another character, to hear his heart pounding during those critical moments. That person--whomever you've based this character on--already has his own life. You need to work on animating the character you're giving life to. And you must remember that because this character is a work of fiction, he must be written as such. Yes, fiction always incorporates some degree of reality to it, but if you're doing it right, it incorporates more imagination than reality.
One thing to always remember that if part of your character inspiration is a living, breathing human being, that person's not going to do what your character's supposed to do. You have to avoid falling into the trap of making your character do what the person has actually done. And god forbid, if that person's in any way involved in your personal life, it's even harder, because you're so emotionally tied to him... He'll do something that you don't want him to do, and you actually start hating your character because you're angry at the person inspiring that character. You can't control him, but you can control your character, and you should take care to control him so that he is his own person, this fusion of your wild imagination and the inspiration behind it all. But the key is imagination. And if you're angry at the person inspiring your character, just know that you can write him so much better...and then do that.
With this one character...I'm going to scribble brilliant colors on top of his solid black lines. I want some of the scribbles to fill in the curved space between the lines, and I want some of the colors to zigzag out of the lines, like lightning bolts, electrifying my little monster a la Victor Frankenstein--only my electricity is words, and my words are colors: the pink and blue of Sea Change, the green of new meadows, the juice of a blood orange, a sanguinal crimson... I will not--will not!--lose these moments.