Or maybe you read the book a while back and you want a refresher.
Here is my #1 recommendation -- listen to the following podcasts (in English) from GTD Nordic in the following order:
(1) What is GTD and how will you benefit from it? (23m49s)
(2) Step 1 in GTD: Capture (23m00s)
(3) Step 2 in GTD: Clarify (27m43s)
(4) Step 3 in GTD: Organize (25m11s)
(5) Step 4 in GTD: Reflect (29m11s)
(6) Step 5 in GTD: Engage (24m32s)
My #2 recommendation is to consider the new workbook: "The Getting Things Done Workbook: 10 Moves to Stress-Free Productivity" (Paperback or Kindle) by David Allen & Brandon Hall. It is easy to read, has great exercises, and is well thought out.