G'day Ryan,
The King Air is a wonderful aeroplane to fly, I would recommend you google the Beech Talk forum, register, then go to the turbines section. There is a plethora of King Air info on there, particularly from a gentleman named Tom Clements. He also has a fantastic book available called "The King Air Book", which offers many flying tips for the machine.
That being said, it's just an aeroplane, 2 wings etc... However, to reduce your time spent hanging onto the tail, get across the magic numbers for type, like configurations, and critical speeds. I can't help you with the 90 unfortunately. There is a 90 series flight manual available at:
Plane Raytheon BEECHCRAFT-KING-AIR-90-SERIES
One last thing, don't allow all the info on the P21 to overwhelm you, remember Power + Attitude = Performance! KISS!
Good luck.