An easy win for rationalists is to avoid actively managed mutual funds. As a NYT article points out:
"High fees, often hidden from view, are still enriching many advisers and financial services companies at the expense of ordinary people who are struggling to salt away savings....even for retirement accounts that are to be covered by the rules, many advisers are not required to act in their clients’ best interests. This means that they are legally entitled to look out for themselves first and recommend investments with higher fees, to the detriment of those who have asked for help....even when fund managers succeed in outperforming their peers in one year, they cannot easily repeat the feat in successive years, as many studies have shown. That’s why low-cost index funds, which merely mirror the performance of the market and don’t try to beat it, make a great deal of sense as a core investment....With fees included, the average actively managed fund in each of 29 asset categories — from those that invest in various sizes and styles of stocks to those that hold fixed-income instruments like government or municipal bonds — underperformed its benchmark over the decade through December. In other words, index funds outperformed the average actively managed fund in every single category....Investors who believe they have found honest and skillful advisers may still want to understand all of this. Not everyone truly has your best interest at heart."