I print the plans on regular ol paper, cut them out with scissors, then transfer them to foam by "coloring" the edges with a fat magic marker. It works well, makes an outline of your part and with fff you put the marker on the skinned side and when you peel it away goes the sharpie marks.
Also x100000 on the multiple passes of low-pressure knife work. The shallower the angle, the easier it gets. I routinely make clean cuts in foam with blades that are barely sharp enough to cut my finger with.