First, max out your employer's retirement plan, find out what the maximum you can put away a year and do it. Next, open an IRA account and fund that with the maximum as well ($5000). Any additional amounts you can possibly put into a savings/mutual funds, do that as well.
Have enough money in the bank to last you for the next 40 years (or however long you plan to live). Figure out how much you need each month, and go from there.
If you set up a good 401k plan you may be able to retire early. Pretty much you just need to save up enough money to be able to live on for many years to come.