It varies from person to person. But here is how I would prepare myself if I am new completely to new a subject.
1. Pick up a good book (how to find? forums again!) and read it cover to cover to an understanding of the technology. Usually it should take a week to complete this task. FYI: I read 100 pages in 3 hours.
2. Now read each chapter and try out few examples. This task takes more time. Again FYI: My prep times for this task varied from 3 to 4 weeks working 10 hours a day, when I was not working
3. Now read specs/API. This is something not everybody likes and really depends on your excitment level. If you are really fired up it should take a couple of weeks to digest this information. Because you need to try out some examples when reading specs.
4. Take a sample
test and find the areas of improvement. This is the point where your actual preparation starts
5. Now improve your knowledge and start taking mock exams. I took one mock exam per day for a week. After each exam I identified areas of improvement and worked on them.
6. Now take the plunge. Satisfaction after you pass is priceless. For everything else ranchers are here
Hope this helps.