Read the book "The Wealthy Barber". Follow the advice contained therein. Don't follow their advice to buy normal mutual funds, but rather buy index funds from Vanguard, or index ETFs in a brokerage account from Barclays or Vanguard.
Research every big purchase you intend to make. Don't feel that you need to buy something just because all your friends are (the fad right now is for people in their early 20s to buy houses with huge mortgages -- and trust me, those who do, likely will be saddled with huge debts and depreciationing real estate for the rest of their lives).
Learn a couple concepts of finance:
1) Time value of money. How to calculate compound interest, net present value, and future value of a series of cashflows.
2) How the income tax system works, including the various types of income (ie: dividends, long-term capital gains, short-term capgains, interest, income, etc.).
You should also know a few things about statistics:
1) Basic probability theory and its applicability to computing an expected result or return. (once you learn this...you will never visit Vegas though!)