kh72,
What flash said, but also, log the miles that you use the car for personal use. When I have a day where I just run personal errands, I log that as well. Your record of mileage should be seamless and contemporary. The IRS must give "great deference" to written, seamless, contemporary records.
I also try to use "minor diversios" from shopper trips to do almost all of my personal banking, shopping etc. If you divert less that a mile or two from the shop route to run an errand, just note "bank stop enroute".
You do not need to deduct the diversion from your business miles!!!
Based in MD, near DC
Shopping from the Carolinas to New York
Have video cam; will travel
Poor customer service? Don't get mad; get video.