There are 3 basic rules you should follow if you want that the Processing Stage fulfills its mission properly:

1. The first item first. Even if the first item is a nonsense and the second is something really important, all stuff should be processed equally. If you go jumping to what you feel like processing, you will get used to avoid dealing with certain things, and the system will not work.
2. One item at a time. When you are processing an item, you should be totally focused on it. Resist the temptation to look at other items or anything else that looks more attractive. You need to pay full attention to each item to make the right decision, and thus leave all the Inbox items well processed.
3. Nothing goes back to the Inbox. This rule reinforces the other two. If you fall into the habit of returning things to the Inbox for processing them again, you will never strive to process stuff properly, what for? And making decisions will not be so important.

Process one thing after another, pay due attention to each one and do not return any of them to the initial situation. Process like a champ.

In GTD, the inbox does not refer only to your e-mail inbox. It is a broader concept that includes all the things you have collected in different ways: tasks you have to do, ideas you have thought of, notes, bills, business cards, etc…

Collecting is the first phase of your personal organization system, in which you try to collect all your incompletes and stuff in one location: your Inbox (not to be confused with the e-mail inbox).

In GTD, the Calendar is used in a very different way than in other traditional time management systems.

People are so used to fill all the gaps in their Calendars to feel that their world is well organized. This system generates several problems:

“There is usually an inverse proportion between how much something is on your mind and how much it’s getting done.” ~ David Allen

It is impossible to reach the state of relaxed control that GTD promises if there are things that only exist in your head. Thinking about the same thing several times is an inefficient way to spend your time and energy, as well as a source of stress.

“Things rarely get stuck because of lack of time. They get stuck because the doing of them has not been defined.” ~ David Allen

You do not manage time. If you have five minutes available, no matter what you do, you will not end up with six.

David Allen calls stuff to anything you have let enter into your world (physical or psychological) that it is not in the proper place, since you have not yet determined the results you hope to achieve and the first action step to do.