The "new normal" of lower returns and interest rates is forcing investors to save more than in past decades and spend less in retirement, said Richard Marston, author of "Investing for a Lifetime". Marston said investors of any age should keep their assets simple and diversified. Most importantly, he advised that they should not stretch for yield in the current low rate environment. Marston recommended devising "rates of saving" that will allow investors to reach their goals by the time of retirement. Finally, he offered tips on how retirees can reach a sustainable level of spending once they stop working.