How much of what to own and when is the crux of the investment battle. In the old days before 2008 there were some age-old general rules for percentages of stocks, bonds, and cash to hold at various ages. That has all been blown away after 2008.
The Boeckh's outline some basic considerations for NOW whether you manage your own money or have someone else do it. This not a complete solution, just a start, but it's very good: