The rules are simple.

If you rolled a double:
You have to use the maximum number of your 4 different individual numbers. (You had to use all 4 numbers if you can, if not you have to use 3, if not you have to use 2 etc.....)

If you didn't rolled a double:
You have to use both 2 numbers if you can.
If you can move one number but not the other, then move this.
And if you can use any of the 2 but not both of them, then you have to play the higher number.