Few things I've learned
1)Do not use a co-signer. If a lender tells you to get one, walk. If they all do, wait until you've built your own credit a bit more. Co-signed loans tell other potential creditors you need co-signers. A loan solely in your own name, paid on time of course, is what shows you're a good risk.
2)If you have unsecured, revolving credit accounts, DO NOT close them after you've paid your balance in full. I used to do this to protect myself from my own spending impulsivity. Cut up the card if you must to keep from using it anymore, but keep the account open
3)Do not go for those "transfer your balances at this super fucking low rate!" offers. Yeah it might save you some money in interest, but opening additional unsecured, revolving credit accounts looks bad on your credit record. Just choose your cards wisely and pay them as agreed.