For American residents the first thing to do is to maximize 401(k) contributions, since they reduce income subject to Federal and state income tax in the year they are made. My wife and I have done that since our 30s -- now we are in our early 50s.
once you retire, you will be paying income tax on the money you take out of the 401k. if you live in a place with little or no income tax that is not a problem. if you live in a highly taxed place that could be an issue, or not?
