Find other stuff to concentrate on aside from the next app or CLI, LOL!
Starting Score: 675
Use as much of your total CL as you like, as long as you have the cash on hand to pay the cards off immediately. Don't ever, ever buy something that you can't pay off that month, unless it's on a 0% or something, and even then, think it through.
To keep your scores up, and possibly to keep from alarming your lenders, pay your cards off before their statement dates, all but one card. That way, they'll all report $0 except for the one. Let that one report something low, and then pay it off before the due date, so that you don't pay any interest.
Basically, just think of your credit cards as slow debit cards that hit your checking account once a month. If you want to buy something, but you don't have the money now, or have it budgeted from the next paycheck, don't buy it. Pretty simple, actually. 
@Anonymous wrote:they still make money off of whoever your spending money on with every transaction
+1
Lenders get "swipe fees" every time you use your card.
So yeah, they're not making any money off of me via interest, but with me, they sure get lots of swipe fees, because I quite literally use plastic for everything other than Diet Cokes at the cafeteria and the Sunday collection plate.
It hasn't been a problem so far, and I've gotten auto CLI's from most of my banks. 
Also, have some kind of plan where you'd like to be (credit-wise) a few years down the road. Don't end up being one of those people who'll apply for a library card just to get their fix.
@drkaje wrote:Also, have some kind of plan where you'd like to be (credit-wise) a few years down the road. Don't end up being one of those people who'll apply for a library card just to get their fix.
I resemble that remark.... 