First, I'm going to have to give Kimber a prize for topic suggestions. Kimber, you get an autographed copy of my next book, A LOVER'S KISS, as well as the prequels, KISS ME QUICK and KISS ME AGAIN, just as soon as I get my copies of A LOVER'S KISS. Email me, 'kay?
Kimber asks: "How do you keep your own emotions out of your writing?"
I don't. I can't. If I'm having a rough day or week or month, the writing tends to be dark and full of angst. If I'm having a fine ol' time, everything seems easier and the writing lighter. I'm much more prone to write banter when I'm in a good mood, for instance.
I don't really see how a writer can prevent themselves from bringing their emotional state into their writing. Consider the source -- it's just us, really. How can how we feel not influence our work on any given day?
However, I think when the book is finished, it's important to step back and ensure that the tone in any given scene is appropriate to both the activity and the characters, whatever the author was feeling the day he or she wrote that scene. If that's not the case? You might have a problem. For example, what's meant to be light-hearted, endearing banter winds up sounding incredibly snarky and mean-spirited because the author was in a foul mood.
But if you're both in the same emotional state? I don't see a problem. Indeed, some of the best books come because the author's deep feelings are expressed through their characters and what happens to them. The key is to have those feelings come naturally through the character, not to impose those feelings upon them.
Will readers abandon you if you alter tone drastically from book to book? Some will, some will love your work for precisely that reason -- the variations excite them and your work will never be "same old, same old". And if your feelings mean you express yourself more powerfully, more deeply, and make your characters more realistic and empathetic? That's a plus, not a minus, in any genre.