According to Fair Isaac Corporation (the company that produces the FICO® score), there are 5 primary factors used to compute a credit score: 

• payment history
• amounts owed
• length of history
• new credit
• types of credit used

Payment History - 35%

Payment history includes your current and past financial obligations (such as credit cards, auto and mortgage payments) with a record of every on-time, late, and missed payments. Payment history is the single largest factor to compute your credit score — which means: paying your financial obligations on-time is incredibly important. 

Amount Owed - 30%

Amounts owed describes the outstanding balance of your financial obligations on your credit report, such as loans and credit card balances. 

Length of Credit History - 15%

Length of credit history is the length of time that you have been making payments. This applies only to institutions that report your payment data to the credit bureaus, such as credit card companies and lenders. The longer your credit history, the more information credit bureaus have.

New Credit - 10%

New credit is the number of new credit accounts that you have recently opened, such as credit cards and loans. New accounts illustrate you are financially active and therefore, can have a positive effect on your credit score. Often times, when you apply for new credit, a hard credit inquiry is used to determine your eligibility. Too many hard inquiries may signal that you're in financial trouble and prevent you from getting approved.

Types of Credit Used - 10%

Types of credit used describes whether the obligation is an installment loan or revolving line of credit.  An installment loan means there is a fixed monthly payment over a fixed amount of time. Credit cards are revolving, because each month has a variable amount of debt and there is no “end date” in sight. If you currently only have credit cards or "revolving credit", you may want to consider diversifying your types of credit used. Having a mix of both is considered healthier than several of one type. For example, having an auto loan and a credit card could be considered better than having just several credit cards.