If you don't know what you're doing stick to index funds, buy and hold.
This time the why of it - basically whims of a single man - is especially scary.
for retirement savings, balance should shift to bonds or similar as you near retirement.
same principle applies to saving for other large events, like a down payment on a house. decrease risk as even nears.
no need to manage this yourself; every roboadvisor will do this for you rather cheaply