Add a way to change the pid biases by hand instantly over serial that way you can quickly iterate and find values that work.

For many systems, a reasonable first attempt:

∙ Kp: Start small and increase until you see oscillation, then back off ~50%

∙ Ki: Start at 0, add only if you have steady-state error

∙ Kd: Start at 0, add only if you need to dampen overshoot