Putting stuff in a calendar. Now that I've started doing it, I'm not sure how people live without it. I have too much stuff going on to remember exactly when things are happening and some of them are scheduled weeks or months in advance. Everything has to go in the calendar app. For things that are further out, I set reminders one week and one day before. Other than that, I also check at the start of every week, and ofc I check whenever I need to schedule something.