This is the simplified list for easy viewing order for Arrowverse!
I have added SupergirlSeason 1 before the crossover episode to the list. You can watch it basically whenever you want, as long as you watch it before Flash S2E18 or after Flash S2E18(I personally prefer to watch it before Flash episode, but both ways work). Also S1E04 and S1E05 were aired ouut of original order. Episode 5 should be viewed before episode 4