I don't know about you but my characters live and breath, I feel when I'm writing that I'm watching their lives and taking notes of what's happening. I think I'm lucky with regards to the fact that my stories play out like movies in my head. I can pause and picture a three dimensional image in my mind, so I can picture things with great detail. I have always had a great imagination and have been told on more than one occasion that I'm weird because of the things I think of. I used to wonder if they were right, but these days I'm comfortable in the knowledge that it's an asset to be exploited.
So I take the time to watch my characters grow, see what directions they want to take. I find that they surprise me which is good because I get lots of comments about my stories not being predictable. When I wrote my first adult novel I had the overall story in my mind and some of the characters mapped out, but it wasn't working. I took out one of the male detectives and gave him the flick, it's always disconcerting doing that because it can sometimes mean a massive re-write. I then put in a female character, the changes were instant and dramatic. the whole dynamic of the story changed, (for the better) but it did drag me out of my comfort zone, now had to write from a female perspective. To increase the pressure, that particular character turned to me and said, "this is now my story, try and keep up." She was a hard task master, I had to write hard to keep up with her pace.
This is why each time I sit down to write I love it, I never know where I'm going and who's goin to be there. I saw a famous author once in an interview say that when he writes there are no surprises, he methodically maps everything out so all he has to do is fill in the blanks. He also admitted that it took the fun out of it, I'm not surprised how boring is that? I have spent the last 31 years of my life doing a boring job. Writing is freedom, writing is fun, writing is now my life, I never want it to be boring or a trial. So I will keep following my characters into tight corners and watching their responses.