I'm not allowed to share details about the exam, of course, but I can share how I prepared for it. The first thing I'll say is that it is not an easy exam. I took it and narrowly missed passing a week ago, and on my re-take today I passed. So the first bit of advice is, be sure to get a Second Shot voucher from Prometric when you're signing up to take the exam - you might need it.
I think the main reason I found the exam difficult is that it was so comprehensive: there's an awful lot going on in Windows 8 and the exam covered a lot of territory. You can see the list of what's covered here in the Skills Measured section. Secondly, I think I faltered a bit the first time around on namespaces - I memorized them more solidly for the second time and I think that helped me better discern right answers from wrong ones.
Here's what I did to prepare for the exam:
• Develop Windows 8 Apps
I've authored about 5 "real" Windows 8 apps, several of which have gone through the Windows Store process successfully. I think you need this hands-on experience in order to be prepared for the exam.
• WinJS Samples
The WinJS samples are really valuable. There are many of them, - most of them short and to the point -- and they are a tremendous learning aid.
Read the documentation. Sure, some of the doc pages are dry or just list class details without much of an explanation - but there are also great conceptual pages.
I also found a lot of good information in blogs when I searched on various topics.
• Walk the Skills Measured List
I went through the Skills Measured checklist and ensured I knew the basics about each skill listed.
• Microsoft Virtual Academy
There are 8 hours or so of videos on Microsoft Virtual Academy to prep for this exam by Jeremy Foster and Michael Palermo - watch them. It's called the Developing Windows 8 Apps with HTML5 Jump Start (note: there's also a jump start course available for the first exam, 70-480).
Jeremy Foster's CodeShow solution contains lots of great samples, all in one Visual Studio solution.
Well, there you have it. Next month I hope to summon the nerve to go for the Advanced exam and obtain my MCSD for Windows Store Apps.