Right now, my writing processor is at 6.5" and I'm writing using Times New Roman and 12 point font. To me, though, the 6.5" is too long and I want to cut it down to make it look more like a book as I'm writing. What can I cut it down to to make it look more like what I want? Is there preference to the ruler like times new roman is the preference for font?
Grab a paperback from your shelves and measure it. Set your rulers and margins to match. Be aware, though, that proper manuscript format (the format it has to be in for submission to agents and publishers) is VERY different. William Shunn's website here has all the details you need.
Microsoft Word has a novel manuscript theme--that sets up almost everything for you. You just need to setup the .5 indents. But it formats your headers, margins, and some other things. I recommend using that and then going to the link Minstrel provided to make the rest of the changes documented there. Ed also gave spot-on advice as well. If you don't use Microsoft Word, then I would still recommend going to the link Minstrel provided and doing it all manually yourself in whatever program you use.
If you'd prefer to format your document like a book (rather than in manuscript format) while you're writing, you can find common book sizes here: http://en.wikipedia.org/wiki/Book_size. I can see that it might be helpful to have it look like a book whilst writing, but it might also create more work for you later on when you have to convert it to manuscript format before sending it out. Your decision, of course.
Another point I would like to make is that when your manuscript is formatted correctly, it translates to eReader's just like a published novel. So if your intent is to read your work as close as possible to a published novel, this is the best way--since it looks exactly the same.
