1. Becoming an investor before you know your net worth.
  2. Buying an investment you don’t understand.
  3. Trying to time the market.
  4. Putting off saving for retirement.
  5. Playing with money you can’t afford to lose.
  6. Paying too much for taxes.
  7. Buying investments that can’t be sold quickly if you need the cash.
  8. Having a 3 year mortgage.  Do at least a 5 year and pay more on principle.
  9. Not asking for professional advice.
  10. Giving total control to someone else.