To not touch a credit card and pay for something you can't afford.
If you can't pay cash or pay for an item within the 30 days before credit card fees apply then I won't buy it. There are a few things that don't work and that is purchasing a house and a car.
Purchasing a house you are penalized because of interest rates and I always get ahead of the payments so it brings the interest down. Any other way and you are giving away hard earned money.
When I was younger I had a credit card and learned the hard way with interest rates and it is not worth it. A purchase can cost you double what you paid for it and that is why I have no credit anywhere what so ever.