Tip #1 - Inadequate Space for USPS Bar Code (4 inches required)
The US Post Office tries to print a 4 inch long bar code on each of your mail item. This bar code assists in sorting your mail items through the Post Office equipment. A very common graphic mistake is to make a very colorful eye catching piece, but not allow room (white space) for the 4 inch USPS bar code. See examples below.

Examples of Good Design	Examples of Poor Design

Tip #2 - Fold Pattern not ideal for USPS Sorting Machines
Self-mailers prepared for "automation rate" discounts must have tabs to prevent the open edge from jamming the high-speed processing equipment used by the U.S. Postal Service. Please see example below: