Tips: I'm in my late 20's but I've never owned a car I didn't pay for myself.
1) Don't finance a car you will not love. A lot of people will tell you to buy this or that and save up for what you want. That's stupid. That's like dating a girl you don't really like and committing to her for a five year relationship. By the third month, you'll hate her guts and you don't appreciate a car you hate. So if you have to go a year or two older or from a driver's edition to a base, do what you have to do. But get the engine and base model you love or at least REALLY like. There's nothing more sadder than someone who wanted a performance car who ended up in a Corolla. I think happiness should be number 1 above feasibility and economic sense.
2) Wait until you make the first payment to start driving it hard/modding. There's a reason for this. When you're young, you feel like you accomplished yourself by making the down payment, signing the papers and driving off the lot. Little do you know, about 50 days later you have to make a payment and it hurts. It hurts less than rent, but a lot more than a cell phone bill. It's a VERY REAL payment to make, compared to the stuff you're used to when you're young.
3) Don't stress if your interest rate is high. If you don't have a great cosigner and you don't have excellent credit or established credit, your interest rate is going to suck. But that doesn't make it a BAD idea to buy. It's less ideal, but to be honest, there's no such thing as a perfect situation to buy a car. It'd be nice if you could save up $17,000 cash, walk into a dealer, haggle to $2,500 below market value, get free mats and a blowjob thrown in but that's not how the world works. A terrible deal for one person is a life saving deal for another.
Two of my friends own WRX's. One of them has parents with an 800 score who bought him a Hyundai Elantra for college paid off. Graduation time they took him to a Luxury Car dealership, traded in the Elantra for $4500 and gave the dealer $4000 cash on top, cosigned with him and he got like a 0.9% rate. They cosigned with him for a $4000 credit card, bought plane tickets with it and paid them off using his bank account to boost and nurture his credit score to a 770+.
Another friend? He cosigned with his parents for their house when his dad got hurt at his job, his mom got breast cancer and he got tied into their medical bills and foreclosure battles. After 2 long years, his mother is healthy, his dad is working and he has.... a 540 credit score. He just started a new job, had $2000 saved up and his car literally died. He was late to work and his boss said, "You've been here two weeks, if you come late again, don't bother coming in at all." We searched and searched and couldn't find a deal on a car to save our lives. Finally we walked into a dealership and he got approved for a WRX for around $20,000 with an interest rate of... 18%. Ouch.
But what else could he do? Scour Craigslist? Get fired? Buy a POS that's just gonna break down again on him?
Sure he's losing like... 40% of his payment to interest but in 5 months, he's overpaid by $250-300 and chopped off over $1500 of his principal. He already called and they said next month he can get his interest slashed in half. But he's HAPPY.
He's a lot happier than our other friend who followed the Ivory Tower idealistic "save save save and fix your credit" advice. That dude is miserable as hell and hates his car.
So that being said, if you have a job, set aside some money for a down payment, walk into a dealership and find out what they can approve you for. Also ask your bank.