These are the Do's and Don'ts...
Remove errors from your credit reports. Eliminate outdated information or unauthorized charges by writing the bureaus and following up with creditors if necessary at least three months before applying for credit. Your FICO score (a credit score developed by Fair Isaac & Co.) and reports from the three major credit bureaus--Equifax, Experian, and TransUnion--are available at Myfico.com for $15.95 per report. Contrary to popular belief, checking your own credit does not lower your score.
You can also receive an annual credit report for free at https://www.annualcreditreport.com.
Look at this page to see your free credit report rights: http://www.ftc.gov/bcp/edu/pubs/consumer/credit/cre34.shtm.
Pay all bills by the due date, even if you are making just the minimum payment. Any missed payments lower your score, whether they're big bills,like the mortgage, or "minor" ones like department-store bills.
Keep account balances below your available credit limit. Ideally, pay off balances every month. Don't max out your credit cards.
Comparison shop quickly. If you are hunting for a mortgage or car loan, file your applications within 14 days of one another. Multiple lender inquiries for a single type of loan will be treated as one inquiry, but if you spread out your applications over weeks or months, you could inadvertently lower your credit score.
Refrain from borrowing entirely. If you don't use credit, you won't have a credit score, and getting credit will be almost as tough as if you had poor credit.
Close old accounts. Long credit relationships are viewed positively in credit evaluations. Closing them may lower your score under some credit formulas.
Apply for many new accounts within a short time period. Resist the urge to take out cards just to get store discounts. This will drive down your credit score. Apply only for loans and cards that you're sure you want.
Combine accounts. Say you have two accounts, each with $10,000 limits and $2,500 balances. If you transfer one balance to the other card, for a $5,000 balance, you have a $5,000 balance on a $10,000 credit limit, so you are using 50 percent of your availbale credit instead of 25 percent. Higher credit-utilization rates will lower your credit score.