The most common investment question I get asked by friends and family by far is: "Can you take a look at my 401(k) and tell me what investments to choose?" While I'm always happy to oblige, the secret is that choosing your own 401(k) funds doesn't need to be complicated -- as long as you know how to identify and avoid your plan's worst investment funds.Your 401(k) allows you to choose which mutual funds you'd like to allocate your investments to, generally as a percentage of your contributions.