Here's a sure-fire way to make your income tax preparer cringe: Show up with a couple of paper bags filled with unsorted receipts.

Getting the refund you are due or paying only what you really owe requires some preparation on your part before you even approach your tax service preparer or accountant.

And a large part of it is having proper documentation.

"I would say about 25 percent of the people don't have all the documents they need when they arrive," said Stephen Gaudino, a Greece, N.Y., accountant who specializes in taxes.

One who comes prepared is Mark Scuderi of Irondequoit, N.Y., who has been a client of Gaudino's for almost a decade.

Scuderi has an MBA and is a financial adviser for Morgan Stanley, which would seem to make him eminently qualified to do his own tax return. But he doesn't.

"One thing I learned in graduate school taking all the accounting classes, the one message I took out of those classes were 'Hire an accountant,' " he said. "That's what you're going to learn, to let someone else take the responsibility for doing your taxes."

Yet even if you do your own taxes — by hand or with the help of available software — being prepared is essential to a migraine-free experience.

Scuderi takes the responsibility upon himself to be fully organized when he arrives at Gaudino's office.

That includes tallying up such things as his electricity and natural gas bills for the year.

"Because I run the Soap Box Derby in Rochester (N.Y.), basically my entire basement is Soap Box Derby world," he said. "So what we do is I take that as a business deduction, so I have to come up with all the information on how much I spent for (utilities) and other household expenses that may be deductibles. Whatever percentage of my house that I use, that gets applied to it."

Not everyone can claim part of their house as a business expense.

But nearly every filer gets a W-2 form from an employer, which lists taxable earnings and federal and state taxes withheld and is the cornerstone of virtually every tax return.

If you don't provide it for your tax expert, your return preparation will be delayed.

Electronic filings are processed more quickly by the Internal Revenue Service, so it behooves someone who is expecting a refund to file in that manner. (A word of caution, though: Depending on your income, there could be a fee for electronic filing this year.)

Tax preparers will help their regular clients be prepared.

"Steve sends out a package to his clients near the end of the year, saying there are some things you might want to consider by the end of the year in order to prepare," Scuderi said. "At that point, I start to get together all my documentation."

One more piece of the 2005 tax return that could slow your process if you aren't prepared: The mileage allowance is two-tiered. Mileage claimed for the first eight months can be charged at 44.5 cents per mile but for the last four months at 48.5 cents.

Just one more calculation to make before you visit your preparer.