Minimize/Maximize current window keyboard shortcut
Solution 1:
Try that:
Alt + F9 Minimize current window.
Alt + F10 Maximize the current window.
If you prefer to create custom shortcuts see this article.
Edit:
Go to: Applications > System Tools > System Settings > Keyboards > Shortcuts.
Choose the Navigation option, then just add. Or:
Solution 2:
In Ubuntu 14 work for me
Ctrl + Super + Up to maximize.
Ctrl + Super + Down to minimize.
Super aka Windows Key