This is pretty much how we operate. No interest. The second half of that is when using credit, be sure you're only buying something you'd have saved the $$ for in the first place. Don't use 0% interest credit just because it's available, use it because you were saving $$ to buy something anyway but now you can get it slightly sooner. This of course can be easily abused and needs a lot of self discipline.I still have credit cards and a mortgage. The biggest change occurred when we made the decision to never pay another penny of credit card interest. We never carry a balance (unless it's at 0%). We do use our cards (we each have our own separate cards and I have a card for business only use) and we pay their balance in full every month - no matter how much it hurts.
So for the past couple of years or so we've paid NO credit card interest. The only debt we have left is our mortgage and a car loan. The value of both outweigh their principal balances. The car will be paid off in June and we have no plans to "run out and buy another one" until the wheels fall off one of the ones we already own.