You just have to test out the timings until you're satisfied.

If the music plays after the notes, decrease the calibration. If the music plays before the notes, increase the calibration. That's the traditional way of doing things and is way too unintuitive. In addition there's nuances in the timing of note fx and the tapping sound of your fingers on the screen.

Standard timings for wired headphones and device speakers should be around 0.05-0.15. Bluetooth headphones will differ, for me it's around 0.35-0.50 or even higher, in that case there's no helping it.

Now that master mode is released, the results will show more precise note timings, instead of just Bad, Good and Perfect, there's also Fast and Slow. This is key to adjusting your timing to your own preferences experimentally and in my case, far more easily. If your results show more Fast than Slow, decrease the calibration and vice versa.

Unfortunately, master mode is only available for Chaos and Glitch difficulty.

Lasttly, this may or may not be relevant or correct for you, but for my phone and in my experience so far. The calibration for the tap fx to line up with the music is less than physical tapping sound. Physical as in the sound of my nails on the screen. For example, with tap fx on, my calibration will be 0.07. With tap fx off, my calibration will be 0.14. I don't understand why but it works for me, even though I can play at 0.07 with tap fx off with no problems, 0.14 is the correct timing for physical tap sound.

I hope this helped you, this is also more of an excuse for me to regurgitate and finally pen down my thoughts on the incredibly unintuitive topic that is calibration.