15% of your score is based on your credit history.
Typically a longer credit history will increase your score. The score considers both the age of your oldest account and an average age of all your accounts.

10% of your score is based on new credit or if you are taking on new debt.
Opening a couple of new credit lines in a short period will hurt this score. If you are planning on buying real estate in the near future, put off buying a car until after it closes. A new car loan can have a big impact on what price of house you can qualify for.

10% of your score is based on types of credit in use.
The score will consider your mix of credit cards, retail accounts, installment loans, finance company accounts and mortgage loans.

30% of your score is based on amounts owed on all accounts.
Even if you pay off your credit cards in full every month, your credit report may show a balance on those cards. The total balance on your last statement is generally the amount that will show in your credit report. The score considers the amount you owe on specific types of accounts, such as credit cards and installment loans. Small balances without missing a payment shows that you have managed credit responsibly, and may be slightly better than no balance at all. Closing unused credit accounts that show zero balances and that are in good standing will not generally raise your score. A large number of accounts can indicate higher risk of over-extension.

35% of your score is based on payment history.
The first thing any lender would want to know is whether you have paid past credit accounts on time. This is also one of the most important factors though late payments are not an automatic "score-killer." An overall good credit picture can outweigh one or two instances of, say, late credit card payments.