This is a tip that comes in handy in nearly all situations, especially if you check your email often.
Emails aren't only used for communicating with others. Emails are a handy way of planning things and staying organized. You should use it as a supplement to post-it notes and planners.
The tip is simple: email yourself any reminders or to-do lists. Don't open it right away or it defeats the purpose of being a reminder.
I find it helpful to email myself reminders before I sleep since I always check my iPad's notifications when I wake up.
The next time you check your email/iPhone/iPad/etc, you'll notice your unread-email notifications. This should instantly remind you what your email was about...or if you forgot what you had to do, all you have to do is open the email to be reminded again.
It's that simple. Whether it's important documents, reminders, or to-do lists, email yourself. Just do it.