I usually put a board in the planer and crank down until the board just begins to move, let it run through, then run it again.
If you are doing a batch of boards, keep in mind they may not all be the same dimensions, so if you can, start with the fattest one first.
Once I get the initial height dialed in, I run all the boards through once, then start the process of cranking it down a little, running the batch of boards, cranking it down, lather, rinse, repeat...
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