Google Keep is the best app I know for taking notes. There are so many other apps on Android/iOS, but most of them are too complex, or I miss some key features.
Googse Keep is a Google Chrome Android and iOS app which lets you have post-its, checklists, and reminders. It syncs automatically and it's by far the best app.
for me, the reminder is the best just add something you do every week, month or other and it will remind you.