> Never own a credit card. They are all scams and are far more likely to ruin your credit than help it.
That's terrible advice. The best way to improve your credit is to actually have credit in the first place. A good credit score is a balancing act involving increasing the length of time you've had credit, minimizing 30/60/90 day lates (or more accurately, not having any), and having a good amount of available revolving credit (but not too much). The point is to demonstrate that you can be responsible with a decent amount of credit for a significant amount of time.
Not having a credit card whatsoever does not help you, it only hurts you. Think about it, if a friend asked you for money, you'd feel more at ease if the two of you had a history wherein he demonstrated that he could promptly repay you, and over a longer period of time paying back small amounts of money, you'd feel more comfortable lending him larger amounts of money.
The best thing to do is to get a credit card and pay it off in full every month. Pretend that the card is an extension of your checking account and never spend more money than you can put your hands on in any given month.