simply observe the darkness (look out into it) and focus on your breathing. Exclude anything else but those things.
This is what I did but so then what ?
My breath felt exceptionally loud and for the blackness nothing happens except the elusive thin gray forms swirling.
When the track ended I stopped my CD player I wasn't in F10 but still I closed my eyes and was able to have the 3D blackness but it faded away a couple of minutes later.