depends. if you are young and somehow have money to invest ... then I might wait for it to settle a bit more and then buy. Of course if one expects the market to always go up and never correct or crash they should not invest at all
A good time to buy....shorts.
I would imagine that there will be a massive QE move, but this can only give a temporary lift.
Retail, entertainment, airlines, any business that relies on discretionary will take the biggest hits.