1) get out of debt - all credit cards & payment plans, except for your house and maybe your car. No investment plan is going to make you more money that you will lose paying interest on loans.
2) Have about 4 months of cash on hand in a safe place, like an interest bearing savings account, for emergencies or layoffs.
3) Participate in your companies 401k plan (or similar) to maximize the amount of pre-tax earnings you can invest. Make sure the money is being diversified rather than being put in one place (such as company stock). Most companies have some sort of match program, which is free money - but only if you are in the plan. Do it.
4) Every year max out your allowance into an IRA. The amount changes yearly, but take advantage of it. Any money you can invest while minimizing taxes is like getting free money.
5) Get a money manager (Merryl Lynch, Morgan Stanley, T Rowe Price, etc) to help you get your initial investment sum allocated in mutual funds that get your money distributed over several investment options, according to your risk levels - you want Large Cap, Small Cap, Bonds, Real Estate, International... you manager can advise you how to balance your risk levels and at the right % per investment area.
6) Set up an automatic money transfer every month to allocate more money to your money manager to add to your investments.
7) At least once a year talk to your money manager about re-balancing your assets.
8) Don't panic when the market dips - keep buying... you are just getting an opportunity to buy at a discount.
9) Wait. Do not touch the money that is invested. Watch your retirement money grow. It is a lot easier to wait & watch than it is to work late in life because you were irresponsible with your earnings in your prime.