My experience so far.

So far I think the best thing I've learned about acting, is what I've learned from the writing I do.
When I get an idea in my head, or even if I've had a bad day and just need to vent; I write a lot of stories based off of how I feel and often combine my thoughts and feelings with things that I watch on TV or see in the streets.
the writing itself comes naturally to me, but not as naturally as the personalities of each character in my stories. I often find I tend to not only write and narrate the storyline, I also tend to put myself into the position of the character who's recalling the events that happen.
To me writing is as much acting as putting on a play.
I often go through the thought processes of each character in turn and make the scenes in my compositions come together on the page; since I often write in first person, putting myself in place of the character in control of the first person perspective makes it almost as if the pen is the director, and my living room is the stage.

I think it's a good tip for pretty much everyone. If you've got a pen and a piece of paper pick them up, and I know for a fact that we've all got a brain (in which lies both the imagination, and the thought process).
The choices we make about the characters we can become and the lives they lead often says a lot about a person and if that character is something you have created on a page, no matter how similar or different they are to you as a person.
anyone can just pull names and an appearances out of thin air and glue them to a page in a book in a way that fits, but it's an entirely different concept to give that character a personality and a voice of their own until you can put yourself in that character's shoes.

So next time you sit down and start writing about a person you just thought up, take my example into heart. Put yourself in that position and make something out of it.