There are a lot of lists out there telling us what not to do with our money, but the list published [1] in the Consumer Reports February issue was one of the most comprehensive I've seen. Each mistake is identified with an estimated price tag, and the 12 mistakes could cost up to $1 million. Pretty eye-opening when they put it like that.

1. Investing too conservatively during retirement: $360,000 to $750,000.
2. Retiring before you need to: $237,000 to $309,000.
3. Launching a divorce war: $49,000 to $188,000.
4. Underinsuring your home: $16,000 to $194,000.
5. Overpaying for your mortgage: $27,000.
6. Carrying a credit-card balance: $5,000 to $23,000.

Six more, so just

7. Maintaining an unhealthy lifestyle: $4,600 to $42,000.
8. Ignoring Roth accounts: $9,000 to $26,000.
9. Cashing out your 401(k) early: $6,000 to $17,000.
10. Underfunding your 401(k): $36,000.
11. Paying needless fund fees: $4,000.
12. Falling for a scam: $100 to you-name-it.

Source [2]