No need for special tricks.
- convert to BW and put weight on green (and maybe blue) channel > skin tone will be darker and pores more visible
- add contrast to taste
- pull down midtones, if skin tone is too pale
- add local contrast
- oversharpen, especially use too high radius, but watch for jagged lines especially in hair - masking can help in this task
Usually red channel is favored in portrait BW-conversions because it usually yields pleasant low contrast look. Green channel will give darker skin tones and more contrasty skin, usually doesn’t look good if it has lots of weight.