(Step 8 is the answer you asked for, and the rest is how to avoid needing tp do it after the first time.)
There may be better ways, but I do the following
so that I don't have to reset the Z axis in software:
1) Begin with the bed leveling screws about 1/3 of the way up from the bottom.
2) Move the extruder to your first position. (Hint: Make G-Code scripts for all four of your corners, and set them as your one-button user defined scripts 1-4.)
3) Make sure that the bed is positioned well enough that you have room in your leveling adjustment screws to get it into place. If you are too far off, adjust your z endstop to get things closer.
4) If using paper as shims, make sure you are using a repeatable size of paper, like standard printer paper. (Don't just use a random piece of junk mail that may not be the same thinckness as other paper you may use.) Personally, I take an 8x11 sheet, cut it into 4@8 x 2.75" pieces and then fold them in half to make 4 identical 8x1.375 reasonably sturdy shims. Set 3 of the 4 aside for when you lose them or wear them out.
5) Place one end of your shim under the extruder, and begin raising the bed leveling screw. Slowly move the shim around while raising the bed until you can feel friction from the extruder contacting your shim. Use the other end to feel how much friction there is. Personally, I try to make enough friction to feel, but never enough to cause the paper shim to bend if I push from the other side of the shim.
6) Move to the next position, and repeat step 5.
7) Once you do all 4 corners, do them again until you feel the friction on your paper shim is similar at all four positions.
8) (NOTE: This step only needs to be done the first time you use a shim of a different thickness. If you followed step #4, this is set once and forget) Now that the bed is level to the extruder, try a few test prints to make sure adhesion is correct. The first line should be a bit squished, but never so squished that it blocks the extruder. If your extruder gets blocked by the bed, tweak your Z axis in software to raise your extruder. OTOH, if your first lines are cylindrical and not squished, tweak you Z-axis in software to lower the extruder.
9) Be aware that you paper shims are wear items. You should toss them after 5 or so levelings because the extruder will leave ruts in the paper when it is too close to the bed.
Edited 1 time(s). Last edit at 03/12/2016 12:17PM by SvdSinner.