Folded paper towel with a drop of paint thinner on one corner will bridge across the flats without going down the V cuts as much as something like T shirt material will. It can leave sharply defined edge staining.

The oak version always looks best to me. But I'm not impartial about that.

One other thing I do is to set the start depth to 0.010" to insure that there is no polyurethane in the shallowest cuts. Stain wipes out of the grooves during clean-up.