The ERN blog had a few nice posts regarding market timing:

https://earlyretirementnow.com/2018/02/21/market-timing-and-...

https://earlyretirementnow.com/2018/04/25/market-timing-and-...

In the second one he simulates a momentum strategy which does pretty well, which can be used along with multiple other signals to increase confidence.

I was thinking of simulating using leverage after these kind of drops to try to increase returns even further.