Most of it from here.

1. Debt for paying consumer goods is anti-investing.
2. Try to have interest deductible. Slash those nondeductible credit card balances as much as possible. Consider using second mortgages, business loans, etc., to keep interest on debt deductible
3. Hold debt service payments at less than 25 to 33 percent of gross income.
4. Don’t buy stuff you can not afford. Do not use credit cards to finance long-term purchases or items you cannot currently afford
5. Pay with cash. Don’t finance or use credit cards unless it is absolutely necessary.
6. Review debts annually. Make sure the interest rates you are paying are low and competitive given changing market conditions, and if possibly refinancing will save you money.