First layer calibration strips.

thingiverse

Slice with whatever slicer you want, and what ever material you're having trouble with. I adjust the live z while printing to ensure a clear start and finish, and also good adhesion to the bed, also good material fusing. I start printing and lower the bed by a little at a time and watch the prints. Taking note of what height I was at for the start strip, and how much I reduced it for each subsequent strip. I then pull them off one by one and see how easily they separate. When I get to the strip that has a clean start and finish with good fusing and not too hard to remove, that's my height.