Do it as soon as possible. If your company matches funds, (free money !!!) max out your contribution to take full advantage of the match. If they don't match, have them take out as much as you can afford!!!
401K money comes out of your paycheck pre-tax so you are getting even a greater bang for your buck...
As someone else said, your HR department has information available for you. It's a great chance for you to save a great deal of money for your retirement.
Good luck...
