Lots of replies and a quick skim through them suggests that they could be published as a book on comprehensive car care! Make sure you copyright this thread
Just to make sure my two-penneth is in there:
One of the best things i ever did was to find a garage that I trust. Lots of the high costs associated with running a car are down to bad advice about what needs doing and when...and it's the labour cost that pushes the price up. Foreign cars can have particular fitment requirements that can mean a small component can cost a lot more than the equivalent for say your bog standard Ford or Vauxhall (OK, I know they're technically foreign too, but I'm sure you get the point - suppliers and parts are much more readily available).
I buy Citroen. Not the greatest cars in the world, but I like 'em and I got my first with a free years insurance. After 12 months of claim-free driving, they then got me a full 65% no claims bonus. Look out for these kinds of deals - especially at your age as the insurance will be a real ******* to pay.
Then I got a really good trade in with the garage I bought it from. Over a few years i established a good relartionship with the garage and i've kept going back. Familiarity has paid off in terms of lower costs and 'honest' advice.
Look for the lowest emission cars you can. My Citroen C5 is a 2 litre deisel engine, but it's a special type called HDi that qualifies for the lowest road tax as it's almost zero emissions. Deisel also gives you much better mileage...probably the one thing that hits your wallet. Buy a cheap car that only does 30 to the gallon and you'll be sorry. Remember too that if you will be using your car as a runabout in a town environment most of the time, that will use up fuel more quickly than longer open road journeys.
Some people swear by cars that hold their value better like Volkswagon. Audi etc. However, these are more exopensive to buy and maintain, and if you I reckon can be a false economy if you work out all the costs over a few years.
If you want a small runabout for Manchester-type driving, I'd look for a something like a deisel Ford Fiesta. The Ka is ok, but the Fiesta is much better bang for your buck and safer too. And remember that cars become subject to MOT at 3 years. Also, don't forget things like parking costs, parking fines and speeding tickets - all too easy to get hit by a sudden additional bill, or ripped off when parking in a city centre.
God, there's loads more, but I'm sure I'm repeating what others have said.
Good luck!