The most often heard complaint among writers today is not enough time. Creating, rewriting, editing and polishing are all tasks that require a large chunk of time as well as focus and energy.
There is no issue for those writers who are independently wealthy with no spouse or children, but most of us who aspire to write are normal people - with day jobs, spouses, children, bills and the rest of the normal responsibilites of life.
How do you find time to write? First of all you must decide whether you can dedicate yourself to starting and finishing your book. If you feel you have this dedication, then you must make time in your daily schedule to work. Writing is work and it must be treated as such. Don't assume you will be able to squeeze it in somewhere between after dinner and bedtime as there will always be something to take it's place - whether it be something important as a late working meeting, a child's ball game or recital or something as trivial as your favorite television show.
Carry your writing with you where ever you go. Pack a backpack with a notebook, red pens, pencils, highlighters, thesaurus, dictionary and a hard copy of your work, and be sure to take it with you whenever you leave the house. If your more high tech than pencil and paper, invest in a roller briefcase for your laptop or purchase a mildly inexpensive word processor like an Alphasmart.
Get creative with your time. Do you have to eat lunch everyday with co-workers or are there days you can grab a sandwich and head to a vacant conference room or park to write. Do you have children who participate in afterschool activities? This is a great opportunity to take your work with you while they're occupied.
Are you a morning person? Get up an hour earlier and spend that time writing. The worst thing you can do is waiting until you have all other tasks completed before you start writing. Are you a procrastinator? Set yourself realistic deadlines in a planner and stick to them.
It is up to you.