Here's a list of what I can remember off the top of my head that affect your credit score:
Length of time for accounts, the longer the better
Bankruptcy
Divorce (i think, not positive on that)
Foreclosure
Late payments
Missed payments
Debt to income ratio
Credit available to credit used ratio (credit cards, how deep you are on them)
The average of your credit limits. The higher the credit limits on your cards, the better. Say you have $20,000 total limit between your credit cards. You are better off having that split between two $10,000 cards than twenty $1,000 cards.
Making a payment to a line of credit that is through a real bank (not a utility company, or buy here pay here car lot, etc) means that every month they report to the credit reporting agencies your current standing. Student loans and medical bills also report.
So long as you aren't late or missing payments, then every month it comes back saying you are in good standing. In reality, you don't actually have to be putting anything on to credit cards at all, or carrying a balance, or any of that like some people say. The key is using it once in a while, because it looks bad on banks to have cards not in use, so they have started closing accounts on people that don't use the cards at all. Using it for something that you buy on a regular basis like gas means that you don't forget to use it here and there, but also that you will be more likely to pay it off every month since the money is already budgeted.
Once you have enough of a credit history, its easy these days to get cards with points or cash back or something like that, so you end up saving a little bit more money that way. After a couple of years of good credit, you will start to see 0% interest offers in the mail almost daily. These can have their uses, but if you might be tempted to use them to buy shit you don't need, just toss them.
Really, the average person should only be using borrowed money for a house and car, and even the car is arguable. Credit cards are only a process to get to that point. Car loans certainly also work but require a larger commitment, which is why I'm not recommending them as part of the process. I will say though, buying a car at a buy here pay here and using them as the lender only keeps you stuck in the circle of no credit/bad credit, and should be altogether avoided unless you are buying the car outright.
also, triple post