I will mention the way I trade the Gaps in Nifty.
Explanation : The Daily ATR of Nifty is usually 90-100 points. Whenever Nifty Gaps more than roughly 2x the ATR. I would look to fade the gap by taking the opposite side.E.G : The day post demonetization day,Gujarat Election day. However if the Gap is less than the earlier mentioned. I would sit out since most of the times it stays sideways. Regular gaps in the direction of the Trend usually points to strength in that trend. Not all gaps can be faded.