I have no idea if 500 is good/bad/indifferent. My suggestion for improving your credit
profile is the following;
1) Have a money phone contract serviced by Direct Debit
2) Get a credit card from a 'normal' bank and use it for day-to-day spending. At the end of the month, pay of the credit card in full.
3) Get on the electorial role
4) don't be registered at the same address as people with bad credit profiles
5) get a copy of a report from equifax/whoever and make sure it is correct. Write to any companies who have passed incorrect data to equifax/whoever
I would really recommend you don't get a car on finance. I was 19 once and made some excellent questionable decisions around cars (and other things).
If you have no bills to pay / 100% disposable income then I'd suggest using
@Jon 's Money Making Tool Kit. It shows you how to make about £1k a month. By the time you are 20 you could have paid for your car outright - a much better place to be.
When I was 19 I'd have not listened to a stranger off the internet, but I don't think it would right for me to comment on this without telling you a car loan will be a millstone round your neck.
I'm not all risk-adverse though. I am telling a 19 year old to get a credit card. You don't want to know what irresponsible things I was doing at 19 with a credit card!