I kinda disagree. If you use credit, and pay it off before it's due, it doesn't cost you anything, and the credit agencies see that you have a good history of using your available credit wisely. That's what they look for..
A history of using your available credit wisely.
That doesn't mean carrying debt. Pay it off completely every month if you can to avoid paying interest. Some folks will tell you that you should keep a balance on your credit cards or mortgage to help build your credit rating, and that's total nonsense. Paying it off every month shows the credit agencies that you know how to use your available credit and don't buy things you can't pay for.
As for not buying something just because it's on sale, that's excellent advice. Buy something because you need it or want it, but avoid the temptation of buying shiny objects.
Also, never go grocery shopping when you're hungry.