The main rule remains unchanged:
- putting the compass away from the source of high magnetic fields
But you can do How to methodically tune (almost) any multicopter using ArduCopter 4.4.x section 4 - Second flight: MagFit and tell us if it helped 
The main rule remains unchanged:
But you can do How to methodically tune (almost) any multicopter using ArduCopter 4.4.x section 4 - Second flight: MagFit and tell us if it helped