Privet Evgeniy,
1st step:
Your steps/mm should be a fixed number so you should calculate what the number should be by using the calculator on this page:
[
www.prusaprinters.org]
2nd step:
Making sure your feedrate isn't too high for the Z-axis and making sure the stepper drivers potentiometer is set correctly (double Z-motors need more power normally!)
Then if you have calibrated your steps/mm correctly, you should also be able to see your ideal layer height, once again on the prusa page I linker earlier.
Last step is to calibrate your extrusion, if your steps/mm are correct, your layer height is correct and your feedrate is correct (so the motors don't lose a few steps by wanting to move too quickly) you should check out if your extruder is extruding maybe too much material. But let's first focus on getting those steps/mm correct.
http://www.marinusdebeer.nl/
