Using the duty officer system helps a lot. Do the mirror universe action whenever it appears as it has skill bonus and gives a lot of experience.
Those two will take you through it quickly. I think tactical characters might have it a bit easier too in that they can get through missions easier. But the above two methods can let any profession go through the ranks rather fast.
The only thing wrong with Mirror is if a L50 is helping a lower level friend level up. Doing that is great for everything BUT Mirror, in Mirror a higher rank will cut the skill points earned to practically nothing.