First of all you need to understand the basic underlying concept of getting everything out of your head and why GTD is different than to-do lists.
Now, that you have the basic concept you understand why traditional to-do lists don’t work you are ready to start the GTD life of stress-free productivity. The first thing you need to do is to set up your trusted systems. We all have calendars and contacts as trusted systems for remembering where we need to be a specific times and for remembering people’s names, addresses, birthdays, email addresses and phone numbers. Now you need to set up a trusted system for all the other tasks or stuff in your life.
A critical part of GTD is capturing your “stuff” whenever and wherever it comes to you. Fortunately, with todays mobile phones we all have a capture device with us at all times.