Hi SilaS
For the attitude controller i can advice you to start with only P,D parameters. (make '0' I and A gains). For the beginning a larger value of 'D' and smaller value 'P' makes your system overdamped. I mean you will see the multirotor is reaching the setpoint you give from the Rc slowly. Then you may increase your 'P' and decrease 'D' with little steps. When you have decide the stabilization is Ok, the reactions of the frame is fast and no overshoot , you may give a little bit 'I' to eliminate the steady state error. But be aware of larger 'I' values makes your system with overshoot. 'I' component of the controller is the part for instance, when you are holding your frame not to turn the desired set point , it integrates and tries to eliminate the steady state error(you are holding the frame it will never reach the setpoint.). Lastly , the 'A' term is the feedforward term and it will try to compansate the dead time delay of the system. I mean the sudden, instant reaction of the frame when a new setpoint is set to decrease the reaching time. These parameters are highly dependent on your system but you can take a basepoint for the starting 'P' and 'D'
values from the example airframes.