The facts I know:
You can't claim public service rates - these are only for employees, you can claim a % of the running costs of the car.
You need to keep full records - mileage of all journeys in year and whether personal or business
You need to keep all receipts of running costs - petrol, motor tax, service etc
You can claim the right percentage of all your running costs
The facts I believe but am not fully sure of:
I don't think the interest on the car loan is claimable
I think you can claim depreciation the way you calculate
Hopefully someone else will clarify the bits I'm not fully sure of.