E is for Everything.
Whether you like it or not, everything that you need to do, everything you need to remember to get, everything you have to chase up... everything goes into your system for staying organized and effective.
That's a lot of stuff, so if you're keeping it all in your head then it's no wonder that sometimes you forget things, or you just feel overwhelmed with it all and can't get anything done.
But don't worry, it's actually a good thing that everything goes into your system - because then if we improve the system, we get to improve everything.
The easiest way to start improving is to get things out of your head. Your brain has far more important and interesting things to do than try to remember that at 4.15pm a week next Thursday you have a dental appointment. Choose a method that fits with your life - be it an web-based todo list or a stack of 3"x5" index cards - and write down all the things you can think of that you have to do.
Then, whenever you take on a new task, or remember something you forgot when making the list, or make an appointment, add it to the list. The greatest benefit comes from being able to use your brain for other things, as you trust your system (knowing that it is keeping track of everything). All you need to do now is keep using it.