You will often see BigShort traders talk about the BigFour or Main BigShort indicators. While BigShort offers dozens of different datapoints to help you trade, the BigFour are critical to learn.
The BigFour
Dark Pools - Off-market trades
Net Option Flow (NOF) - Selling and buying of puts and calls
Momo (and Shadow Bars and MomoFlow) - Momentum traders like retail or non-algorithmic institutional money
SmartFlow - Algorithmic money