MrShutterBug has the most brief to the point youtube video.

Finally, after eons of Joshua Bardwell telling everybody to just use defaults or reduce filters until motors are hot, MrShutterBug acknowledges that BF defaults are for 4S 5" *only*.

If you are new to PID
* DONT copy/paste
* 80%+ of youtube and forum PID tuning advice is garbage (P=100, turn off filters, BF3.5 is better,).. especially if its based on "feel".
* DO read the BF tuning notes
* make small changes, 1 thing at a time.
* if you can, do use Blackbox and PID Analyzer. If your FC doesnt have it, OpenLog and OpenLagger

And finally.
You CAN test PID in drone simulator games!
Test flying low rates.
Simulator even does great job simulating heavier battery and voltage sag.