[dahdum]

Simplest way is to have information others don't. Much more difficult would be information they have but aren't using correctly.

One example I've heard before is this (maybe garbage...). Publicly traded ecommerce company is going into the peak holiday weeks, and analysts are bullish. You found informational leaks of KPIs by digging through html source code (incrementing order ids, cancellation ids, etc). These KPIs show a downward trend in the final few weeks. You posit these are real, and short the stock since they're likely to miss earnings.