The first step that should done--and the one most people skip--is getting a good idea about the amount of money you'll need for retirement. This isn't a time for guess work. According to MSN Money, not even 40% of people use a reliable strategy to determine how much money they'll eed to retire. Setting a goal for your 401k is one of the most important parts of 401k planning. Since there's no set amount of money that will work for everyone, start by analyze all your future sources of income, including pensions and Social Security. Next, try using a retirement income planner online to help you figure out how much you'll need. You can find a number of these online worksheets in the Resources section below. Consider your age when using these worksheets. Some are designed for younger people while others take into account an older, near-retirement age. Fidelity Investments, in particular, gives each age group their own worksheet to use.