Dammit’s adventures in mountain biking

Set the recommended air pressures first.

Then set the rebound and compression in the middle of whatever adjustment they have ( in your fork's case, I'd leave the compression setting on 'open' ), and make one small change at a time, whether to air pressure, or rebound. The rebound won't be too far off the middle setting, if you have the correct spring rate. You'll then be able to tweak it to whatever type of trail you're riding.

Then find either a long flight of steps, or a bumpy/rocky/rooty downhill section of trail, and keep repeating it, over and over; trying a slightly different setting or air pressure on each run.

Take notes of all this