Know ahead of time what the IRS allows

The IRS has specific rules for which expenses-per-mile you can--and can't--deduct. If you're audited, it will be up to you to prove that your declared expenses are legitimate and documented. Knowing the rules ahead of time makes it easier to keep and organize the paper trail required for each road trip.

I recommend: The IRS spells it out, at length. Look for the rules governing allowable car expense deductions, along with specific examples, beginning on page 15 in Publication 463.

Track expenses and organize receipts

The IRS will want proof of your miles driven or your actual expenses (you can deduct only one of the two). It's more important THAT you keep careful records than HOW you do it. Low-tech or high, the more organized your records, receipts and supporting documents are at tax time, the better.

I recommend: If you're a techie, consider tracking your expenses on your PalmPilot, download the free Gas Mileage MPG Tracker or test-drive MileTracker Pro software. If a simple log book or filing system is more your style, look into Office Depot's log book, storage and filing systems.

Find the lowest gas prices where you'll be driving

Wandering from gas station to gas station at an unfamiliar destination is definitely counter-productive and costly. Know before you go where gas is cheapest.

I recommend: Log on to detailed gas pricing information and enter the zip code(s) of the places where you'll be doing business.

Get professional help

If you lack the time or the inclination to decipher all those IRS regulations on deducting car expenses, get professional help.

I recommend: Find a CPA firm in or near your home base zip code, talk to a tax specialist at H&R Block or contact the friendly folks at the IRS.