Risk management for the home investor?

I know enough about investing to know that to do it properly, you need to consider your return in the context of the risk you took to make it. Riskier investments might return more but they might also bankrupt you and being blind to that leads to chasing returns and ultimately inevitable bankruptcy. Now, a proper investing firm will have trained people with math degrees and decent computers doing risk management for them. How is an average person at home supposed to calculate their risk? Is ther