First Print with the Simple - 3D Printing: Build your Own 3D Printer and Print your own 3D Objects - page 93

One of the secrets to a good print job is getting the nozzle as close to the print
bed surface as possible so that it lays down a flat bead of molten plastic during the
initial movements. To do this, Printrbot recommends cutting a small square from
a sheet of 8.5” x 11” paper. Place this slip of paper under the nozzle tip and lower
the nozzle until it requires a slight tug or two to pull the slip of paper out from
underneath the nozzle tip. You'll have to experiment a few times until you get the
right distance figured out, but as a rule, I lower the nozzle as far as I can get it
without it digging into the print bed's surface. Figure 5.13 shows how I've placed
this slip of paper underneath the nozzle to get the proper distance from the print
bed surface.
Figure 5.13 Slip of paper underneath nozzle.
If you find that the slip of paper is too tight and can't be pulled away easily, use
the 0.1 button for the Z axis to move it up a tenth of a millimeter, and try again.
When you've got the nozzle in the proper X, Y axis location and the right distance
from the print bed surface, tap the Set Home button shown in Figure 5.14 .