Don’t be put off by ‘Windows Store apps’ in the title. There’s lots of really good information about designing for tablets in general here.
Aside: I spotted this in the ‘Windows 8 touch posture’ section:
Because slates are most often held along the side, the bottom corners and sides are ideal locations for interactive elements.
That’s a big difference between iPads and Microsoft’s Surface ‘slate’ (do they actually still call it that?). Microsoft sees the 16:9 Surface as a landscape device, whereas a 4:3 iPad is for use any way up.