The day before your flight
24 hours before your flight, you can check in on the app or the airlines website.
After that, take a quick look and see if they have a departure gate or terminal listed. Some airports have multiple terminals that aren’t connected (JFK has 6), some have terminals that are connected (Atlanta has 7), and some have a single terminal. Most of the time, you can skip this step, since the terminals are connected, or there is only one terminal. But for some airlines at some airports (cough jfk cough) it might be very difficult and time-consuming if you show up at the wrong terminal.
Clean your house. The only thing worse than cleaning your house before you leave is coming home to a dirty house and having to clean it.
Charge your phone, make sure your bags are packed, and you have your ID.