Keeping it around 30% is actually not that good. Keeping your balances below 10% is really what drives the score up.
How I know? Two years ago I literally did not have a credit car at all, had to pay $200 to get a $200 limit credit card (I did get the money back in a year). Now, I have ~780 score, with more than $25,000 credit limit, including a car loan with monthly payment of $230 a month, at 2.59 APR.
What I really focus on!
1) All payments on time, even if they have to be minimum payment.
2)Do not get a lot of hard inquiries because they do stay around for a good period of time.
3)Only open a new account/credit card if you really need it. Opening many of them will bring your age of accounts down.(Again, a lot of hard inquiries over small period of time, no good!)
4)Pay more on your car loan/mortgage even if it's only $10/$15.