Short term moves and also many long term moves are precipitated by some news event.
If you everyday systematically identify 3 to 5 opportunities from the news released after hours you will find good day trading opportunities.
Some of the news is not just for one day it can have multi month effect. So you can use for position trades also.
For example RAX after close released news about management change and it's intention to remain standalone business. As a result it is down big after hours.
Tomorrow most day traders will be actively trading this stock on both long and short side.
The same news has potential to lead to further down move in next few months. So position traders would also be looking at it.
X is another stock with big news after hours and was up on news. Related sector stocks will also be in play tomorrow.
Like this in process term if you study news daily after hours and pre market you will find good trading candidates.
This is a skill which one can build over time if you want to trade these kind of stocks.
All the information needed to do this is freely available. All it needs is a bit of elbow grease.
Earnings After the close today
Earnings Tomorrow before open
After hours movers