Copper balance
The overall copper density should be relatively uniform across the entire board in order to prevent over-etching of fine lines while large copper-free areas etch to completion. If one region of a board has a high density of fine lines, it is important that wide tracks are used in less dense areas in order to prevent from over etching.

Ground planes
Use a sold ground plane. Use of stripes and cross-hatch reduces the functionality of the ground plane and may increase problems with copper balance. If your CAD software fills the ground plane with a series of lines, choose a relatively large line width for the fill segment. Large regions filled with thousands of lines will delay production.