I need help please

Hello warrior friends!

I am dusting off my first char from vanilla wow and have a couple of questions that maybe someone could take the time to answer.

What is arms stat priority for arenas?

And when overpower and mortal strike both light up, which do i press?

Thank you powerful warrior friends.

edit: or can anyone point me to a good up to date youtube guide?

Vers > crit > haste > mastery.
MS always first.

thank you Azeryan