If you have a single member LLC, then there's a good chance the vehicle you drive "on the clock" is the same car you drive "off the clock." If a separate work vehicle is not a viable option, then writing off expenses on your personal vehicle is a great opportunity for tax savings, but like all tax regulations, it’s not as easy as it sounds.
The IRS states that you need to record every deductible mile you drive. So, unless you want to strap a clipboard to your steering wheel and start writing down the mileage to and from every work destination, you should check out Bonnie Lee's article, "How to Write Off Your Vehicle Expense." Bonnie Lee is an Enrolled Agent representing taxpayers in all fifty states, at all levels within the IRS. Her article offers some tips for some basic record keeping that could prove to be invaluable when trying to trace back those "business miles" come next tax season.