1. hold on to your oldest card ...for dear life. age of credit history counts toward to your score (moreso than if you close more recent cards)

2. call your credit card companies and request an increase. your goal should be to have the maximum amount - even if you never plan to use it.

3. doing #2 will help with your debt-credit ratio. you don't have to pay off your cards every month... you do need to make sure your ratio is below 30%. if its higher than that- that should be your priority.
getting an increase is one of the easier ways of getting there (in tandem with lowering your overall debt)
(im in gradschool with no regular income (thanks useless ass hopkins) and its been a struggle sometimes and this immediately affects your score)

4. if you have a capital one credit card- they have a very useful credit core simulator that tells you impact on your score if you pay off (or add, i believe) certain amounts

5. you can maintain zero balances on your cards- its not a use-it lose-it type deal (in terms of your score- i don't know about store cards- last one i had was bestbuy in college and had to close that cause i was being foolish)

6. get mint.com -i cant recommend this enough. its a great way to keep all your finances in one place and has useful budgeting tools
i havent found anything better in the almost 10 yrs i've been using it

7. everyone advices pay the minimum, at least. yes. i say, pay the minimum when its due... plan to make an additional payment before the next statement period. that is if you cant just do it once.


add on....

#edit: avoiding CC's is the worst thing you can do. at least keep one card open. age of credit matters.