I moonlight doing taxes during that season, so I'm as qualified as anyone to comment on this. You can deduct either vehicle expenses OR mileage directly related to your business. If half your annual mileage is personal you can only deduct the other half of expenses or mileage. Vehicle expenses include depreciation, gas, tags, oil changes, reapairs, tires, insurance, signs, etc. If you decide on mileage, then you cannot deduct any of the above expenses. If you use the vehicle for any personal mileage, then you need to keep a daily log of either the personal use or the business use, rough estimates do not fly during an audit. Depreciation is a slippery slope because when you sell the vehicle, the sale price (asset salvage value) gets counted back as income in the year you sell it. Personally, life is much easier if go the mileage route instead of expenses, though there are exceptions.
Also, the mileage rate for the IRS is $0.405 for any miles before September 1, 2005 and $0.485 for any miles September 1 onward, not $0.48 for the whole year.
I haven't touched on any other business expenses (business licenses, advertising, flyers, business cards, uniforms, etc) because they have nothing to do with vehicle deductions, keep them separate when deciding which way to go: expenses or mileage. Your total expenses get deducted from your income and the net is subject to federal, state if applicable, and social security / medicare taxes.
If you have a garage used exclusively for your business (and in theory are properly licensed to conduct business out of your home), you can deduct a portion of your motgage , utilities, etc that is proportional to the size of your home. Same goes for a home office that is used exclusively for your business with certain rules and limitations.
If you are showing greater expenses than income for 3 out of 5 years, the IRS assumes that this is a hobby and frowns upon you attempting to write off a hobby.
Tax preparation is not for the weak of heart and is best left to the professionals that can do it more efficiently. You could spend an entire weekend searching the IRS website instead of detailing one car in a half a day to pay someone to do it for you. I personally hate it and charge more when I get a shoebox full of unorganized (or unrelated) reciepts as it takes longer to sift through it all.
But, if you're inclined, I'd start off with this link for the IRS FAQ for small business:
http://www.irs.gov/businesses/small/article/0,,id=135419,00.html
Good luck!