Put as much money as you can into tax-sheltered retirement accounts, such as 401(k)s and IRAs. That's because the investments in those accounts grow tax-free until retirement - meaning you'll wind up with way more money in your old age than you would have otherwise.
You'll also save taxes on money you contribute (if you choose a traditional 401(k) or IRA), or on money you withdraw (if you choose a Roth 401(k) or Roth IRA).
