Charge -> Rend is your basic opener. Mortal Strike will take care of keeping Rend up through the Lambs to the Slaughter talent.
After which:
Colossus Smash > Mortal Strike > Overpower > Slam
Colossus Smash procs through Sudden Death should be used to maximize up-time, you do not want to clip the duration of CS. If you have CS up and Sudden Death procs, wait till your current CS drops and then refresh it.
Slam should be used when the other options on your priority are on CD, however if you have less than 1 second more Mortal Strike to become available, you wait and use Mortal Strike rather than Slam.
Heroic Strike should only be used when you have 70+ rage, during Deadly Calm or on Battle Trance procs.
After which:
Colossus Smash > Mortal Strike > Overpower > Slam
Colossus Smash procs through Sudden Death should be used to maximize up-time, you do not want to clip the duration of CS. If you have CS up and Sudden Death procs, wait till your current CS drops and then refresh it.
Slam should be used when the other options on your priority are on CD, however if you have less than 1 second more Mortal Strike to become available, you wait and use Mortal Strike rather than Slam.
Heroic Strike should only be used when you have 70+ rage, during Deadly Calm or on Battle Trance procs.