If you're worried about risk and being able to sleep at night, you can dial back from 100% equities (S&P 500, Russell 3000), and do some bonds. Vanguard (e.g.) has funds that are fixed 80/20, 60/40:
> Cash in the bank so you can buy equities at the bottom.
JFC, this is the dumbest possible advice given this thread.
If someone thinks equities are overpriced and one thinks the value of USD is decreasing, then 'cash in the bank' is an equally bad answer to 'buy equities now'.
The correct answer, given those beliefs, is 'buy commodities' (or scarce assets).
Or a mixture of cash and gold or another hard asset / inflation hedge considering the US dollar already eroded 10% this year and Trump openly wants the dollar to devalue further.