Most:
-Breathe from inlet side (flame trap/kidney box)
-Breathe from rocker cover
-Return to exhaust side

Ideal way:
-Breathe from both sides of the block
-Breathe from rocker cover
-Return to sump below oil level (get a fitting welded into the sump, with one way valve)

Breathing from the rocker cover is optional on both, some say do it, some don't