One thing in Mac that alwaysssss irritate me, is the application switcher.
Imagine you have 2 applications, A and B. A is a single window fullscreen and B has 2 windows one occupying the left half of the screen, the other occupying the right half of the screen. Lets call them B1 and B2 respectively.
If you try to put A at the back of B, and want to place B2 on top of A so you can work on it while looking at content of A, you can't do it by simply using Cmd + Tab.
Cause Cmd + Tab will put both B1 and B2 on top of A. So A's view is now hidden and you can't work on B2 cause your content is hidden.
The solution is simple.
Lets say A is selected and on top of the screen now.
Cmd + Tab and highlight B. But before releasing the Cmd key, press Ctrl + ↑ and you can now select B2 directly!
Not sure if its obvious, but I hope it helps others who has the same problem as me.
Bonus: Here's more tips for you http://www.cnet.com/how-to/handy-tips-for-mac-application-switcher/