do you use AllAboutBirds (CornellLab) as a resource? Once you’re on a species page, you can find a section where you can ‘Compare with Similar Species’. That will give you specific tips on what to look for which might help.
And I agree that songs help (or are necessary). You can try recording the song or trying to make notes you can add to a photo. The Cornell site has info on songs, as well.
For myself, I’m learned to be content with genus level IDs for a lot of my Flycatcher obs.