When you use a personal vehicle for occasional business use, you can claim your mileage using the standard mileage rate method or the actual expense method.
To use the standard mileage rate method, you can claim 54 cents per mile of business use. This includes allowances for gas, maintenance, and other expenses. You must keep a diary, log book, or use a tracking app that records the date, mileage, and business purpose of each trip. Regular commuting is not deductible.
To use the actual expense method, you must record the mileage as above, plus you need the total vehicle mileage for the entire year (starting and ending odometer reading). You also need to keep track of all your vehicle expenses -- gas, maintenance, repairs, insurance, finance costs (interest, but not principle) and depreciation (wear and tear). You figure our the business percentage of vehicle use and deduct the same percentage of your expenses.
In most cases, the standard mileage method is more generous.
No matter which method you use, you can separately deduct tolls and parking expenses that you pay (but again, NOT for your regular commute.)
See chapter 4 of publication 463 for more information https://www.irs.gov/pub/irs-pdf/p463.pdf
