Formal Education
Not worth the money, most of the time.
Return on investment
If you are going to pay a significant amount for an advanced degree, you better do your homework and make sure you can make enough money with that degree to justify your efforts. Use common sense here, a Computer Science degree will pay far more than an English degree.
This website is a good resource for showing how much you can make with different bachelors degrees.
(if possible) Make your employer pay for this
If you have the ability to have your company pay for college courses, feast on that buffet!
Increase your Savings Rate