Everyone has their "preferred" way of running the screws. It is all based on top, mid or bottom end. There really is no magic bullet. Experiment.
As a general rule the closer the adjustment screw is to the manifold will provide more bottom end. Also the more water introduced = more bottom.
Top end:
Close top and mid screw and open bottom screw until water
just sizzles on chamber.
Bottom end:
Close bottom and mid screw and open top screw so the chamber is hot to the touch (but no sizzle).
How I've always run my FPB:
Closed mid, open bottom till sizzle then open the top screw till pipe is hot or warm.
I like to balance the water between 2 screws so if one gets clogged, it won't melt hoses.
As always, YMMV
FYI:
Download manual here