If you want to use the standard mileage rate to calculate vehicle expenses, you must choose it in the first year you use the car for business. In later years you can choose to use the standard mileage rate or switch to actual expenses.
Once you use actual expenses for the vehicle (even if it's the first year you used it for business), you can't switch to standard mileage rate. You must continue using actual expenses as long as you use that car for business.
If you use the standard mileage rate, you must have records of business versus personal miles driven.
If you use actual expenses, you must have records of all expenses and must allocate those between business and personal use.