Recent tallies show almost a third of U.S. credit scores fall below 649. While not impossible, acquiring a mortgage loan will likely be more difficult and more expensive at this level than with higher scores.

Here are the fundamentals to guide you in establishing and maintaining a healthy and legitimate credit score. 

The somewhat obvious:

• Borrow only what you can afford to repay.
• Make all of your payments on time.
• Avoid excessive requests or inquiries for credit.
• Have an emergency account to pay for unexpected expenses.
• Check your report annually to contest and remove any erroneous information.

The not-so-obvious:

• Do not open new store credit cards just to save on a purchase. New accounts can lower your score, and too many payments can be difficult to manage. Saving 10% on a $300 lawn mower means little if it costs you even just fractionally more on a $300,000 home loan.
• Do not open new accounts just to transfer balances for an introductory rate. In addition to possibly lowering your score, these offers often have traps. Instead, use them to leverage a lower rate from your existing card company.
• Do not close old accounts. If you have a good record of payments on old accounts, these will benefit your score. Using them occasionally and conservatively will keep them active and contribute toward a good score.
• Do not be afraid to use credit. Without the use of credit, you will have no score, and that can be just as bad as a low one.
• Keep a high credit line and a low balance. Credit utilization ratios measure this relationship, and lower is better.
• Maintain a variety of account types. A combination of revolving, installment and secured financing along with excellent records of payment will yield a higher score. Still, don't run out and open an account just to have diversity, as this is the least influential factor.