I have used Windows for all of my life. In Windows, shortcuts are (almost) always initiated with the Control key. Modifications to those shortcuts are then done with the ⇧ key. So, for example, you move to the next tab using ControlTab ↹ and move to the previous tab using Control⇧Tab ↹.
I have recently moved to OS X and I'm having a hard time remembering when to use ⌥ and when to use ⇧ in combination with ⌘. I almost never get it right. It is like it is random, but I want to think there is actually a rule.
So, does this rule actually exist?