A friend of mine asked me how to learn about GTD (Getting Things Done), so I thought I'd help out by writing a post on how to get started with GTD.
First, you need to learn what GTD is! You'll want to read the book by David Allen once and then put it aside and think about it. The book is really abstract and encompasses many concepts (like theoretical physics, but not quite that hard). It will help to review parts of the book as you go along implementing your GTD system. The GTD Primer provides nice summaries of each chapter in David Allen's book. It may also be helpful to take a look at the GTD FAQ and the 43Folders getting started guide for a basic overview of GTD.
The first task is to collect all your loose ends (mental and physical) and sort them. It's called a "mind sweep".
Next, you'll want to come up with your own implementation of a GTD system. For some inspiration, you may want to see what other people have done. Some low-tech pen and paper systems: the Hipster PDA, the Moleskine PDA, how to make a GTD system for $20, Patrick Rhone's productivity whitepaper, the D*I*Y planner, my Cross ion pen and index card capture device. As for software systems, I've only used two tools: Backpack and todo.txt. Backpack is a great web-based GTD system (Patrick Rhone has a description of his Backpack GTD system). For those of you who are into Unix and command line like me, I really like Gina Trapani's todo.txt script (my current system). Download Squad has a feature article on GTD software tools and Wikipedia also has a table comparing various GTD software. If you want to procrastinate, you can look at this epic list of GTD tools.
As you spend more time developing your GTD system, you'll probably mess up and get off track. Don't worry if you fall off the wagon. It happens to everyone and the best part of GTD is that 1) it gives you breathing space to get back on track and 2) it's easy to pick up from where you left off. The most common pitfall is failing to do a thorough weekly review (or not doing them at all). Here's an article about how to go about doing the weekly review (Lifehacker has a shorter process for the weekly review). Another problem is poorly written to-do lists. 43Folders has a post on how to build a smarter to-do list. Remember that you can *not* do a to-do item and just cross it off the list. To-do lists aren't the end of the story; you also have to choose your priorities skillfully (what to-do next?). If you've come up with a wonderful GTD system for yourself and have mastered your to-do lists and weekly reviews, it might be time to examine your life goals (the "30,000 ft level" mentioned in David Allen's book). Steve Pavlina has some good advice in "how to discover your life purpose in 20 minutes", "setting your primary focus" and "living your values."
Finally, if you want to get some advice from the guru David Allen himself, check out his podcasts with Merlin Mann on 43Folders (the Productive Talk series). Another set of excellent podcasts about GTD is the first 12 episodes of the Fisher Files (the first episode "Introduction" is here). The Fisher Files is hosted by MIT physics professor Peter Fisher and has an academic leaning to it.
If podcasts are not your thing, check out 43Folders Recap: Best of Getting Things Done.