I think this is a good question with no single right answer. For a conservative investor, possible responses to low rates would be:
- Do nothing. Stay in cash, and accept the lower returns.
- More to risky investments, chasing higher returns.
Probably the best response is somewhere in the middle: consider riskier investments for a part of your portfolio, but still hold on to some cash, and in any case do not expect great results in a bad economy.
For a more detailed analysis, let's consider the three main asset classes of cash, bonds, and stocks, and how they might preform in a low-interest-rate environment.
(By "stocks" I really mean mutual funds that invest in a diversified mixture of stocks, rather than individual stocks, which would be even riskier. You can use mutual funds for bonds too, although diversification is not important for government bonds.)
Cash. Advantages: Safe in the short term. Available on short notice for emergencies. Disadvantages: Low returns, and possibly inflation (although you retain the flexibility to move to other investments if inflation increases.)
Bonds. Advantages: Somewhat higher returns than cash. Disadvantages: Returns are still rather low, and more vulnerable to inflation. Also the market price will drop temporarily if rates rise.
Stocks. Advantages: Better at preserving your purchasing power against inflation in the long term (20 years or more, say.) Returns are likely to be higher than stocks or bonds on average. Disadvantages: Price can fluctuate a lot in the short-to-medium term. Also, expected returns are still less than they would be in better economic times.
Although the low rates may change the question a little, the most important thing for an investor is still to be familiar with these basic asset classes. Note that the best risk-adjusted reward might be attained by some mixture of the three.