General items.
Have re-read the article: Measurement of the photon identification efficiencies with the ATLAS detector using LHC Run-1 data.
And read the ATLAS note : Electron reconstruction and identification efficiency measurements with the ATLAS detector using the 2011 LHC proton–proton collision data.
Understand the tag-and-probe methods for electron selection.
The next step is to learn the framework of electronic tag-and-probe, and be familiar with how to select samples through the program.
Anything else?