NEW YORK (MONEY Magazine) - Ways to make yourself more attractive to lenders. Five factors determine your score. Knowing what's most important can help you raise yours.

A full 25 percent of reports have errors serious enough to deny you credit, according to the U.S. Public Interest Research Group, and it's up to you to fix them. Your credit report includes directions for filing a dispute.

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What goes into your credit score?     Bills paid on time  35%  Ratio of debt to credit limit  30%  Length of credit history  15%  Credit application  10%  Variety of loans  10%   Source: Myfico.com.

For mistakes such as a misspelled name, contacting the bureau by phone or online is fine. For anything else, write a certified letter with return receipt requested. With a free report, the bureau has 45 days to investigate your claim. In the meantime, contact the creditor who erred as well.

You have the option to add a 100-word statement to your credit report that explains your side of the story -- a dispute with a lender, say, or a bankruptcy.

But think about how online mortgage lenders work. You type in your personal data and within a few minutes get multiple offers. It's all computerized. There's no one taking the time to read your carefully crafted defense of why a bill was late.

Even when there is, a statement may not help and can occasionally hurt.

"People do more damage by admitting to their bad behavior," says Stephen Snyder, author of "Do You Make These 38 Mistakes with Your Credit?" "It validates the fact that it's actually true."

Nothing is more important to your credit profile (see the chart). Missing your credit card's 2 p.m. deadline by even a few hours can trigger a $39 late fee.

That's not all. Once you're late, that issuer will hike your interest rate into the stratosphere, and after 30 days report your slip to the credit bureaus. When other lenders take a look at your file, which they do from time to time, they may raise your rate too.

Adding a child to your credit card can help his or her credit but sabotage yours. If your kids can charge on your account at will, and their wayward spending makes it tough for you to pay the bills, both of you may end up regretting your leniency.

How much you borrow vs. how much you can borrow, or your utilization ratio, is the second most important factor behind your score. Using 30 percent or less of your available credit is best. More than 70 percent is a serious drain on your score.

You can reduce your utilization ratio in two ways: Pay down what you have borrowed or expand what you can borrow. To do that, raise your credit limits or open a new card. Just be sure you resist the urge to borrow more simply because you can.

Even paying your bill in full every month doesn't guarantee a low utilization ratio. How maxed out you look depends on your balance the day your issuer reports to the bureaus.

If that's right after you've made a big purchase but before you've paid your bill, your score suffers, notes Evan Hendricks, author of "Credit Scores and Credit Reports." For 60 days before you apply for a loan, put off any major shopping trips.

The most valuable accounts are your oldest ones. If you cancel credit cards that you've had for a long time, for instance, you may take a file that's 20 years long and reduce it to four or five years.

To make sure a card company doesn't try to get rid of you -- you could be costing them more in postage than you're producing in fees -- use the card every three to six months.

You can be docked for having a finance company listed among your creditors, says John Ulzheimer, a credit expert at lifeafterbankruptcy.com.

"Finance companies are the lenders of last resort," he notes. Think you've never used a finance company? You may have if you have ever borrowed for a purchase (furniture, say, or a computer) through the store.

A flurry of credit applications hurts you. Don't worry about shopping around for a mortgage or a car loan -- multiple applications you make within 14 days for either loan count as only one. But those cards you apply for to earn 10 percent off at the mall? Big mistake.

When issuers compile prospects for junk-mail campaigns, they make a "soft" credit inquiry, which has no impact on your score. However, it doesn't give them enough information to close the deal. For that, you have to send back the application, giving them permission to do a "hard" inquiry.

That counts as a new credit application and can take your credit score down a handful of points.

Step 3: Protect your good reputation