On the expiry day, Market movers will move the price based on their positions. We never know how they are going to move (up or down). So, What we can do?
We can monitor the number of open positions using Open Interest and follow the option sellers.
Price Decreases and OI Increases -> Option sellers are gaining money
Price Increases and OI Decreases -> Option sellers are losing money
Check the Banknifty option chain in NSE website and see the Change in OI column for each strike price.
If price decreases and Change in OI is greater than 400000(20000 lots), then most likely option sellers will win. You can sell the options and put the S.L as intraday high. If the change in OI is keep going up like 600000,700000 then mostly the option will expire as 0.
You can exit the position either if S.L hit or Change in OI falls below 200000(10000 lots).
Please remember that the data is bit delayed on NSE website and the big traders use automatic trading software to move the price. So within a minute they can add lots of positions. So, always put the S.L.