You need to total all of your bills for a month, including all groceries.
When you've done this, clear a credit card and have it changed to one that either gives you cash back or points to use for purchases or airline flights, whichever you want more.
Keep track of all your utilities you can tie to the card and all of your monthly purchases, just like you would use a check-book.
At the end of the month, pay off all but $15 (to fool the computers into believing you have a continuing active card and it's used every month). Earn max return.