The USPS PCC put together a great "workshop in a box" detailing the most common mistakes in mail piece design and how to avoid them. Some of the most prevalent mistakes in the industry are:
The 10 most common mistakes encountered are:
1. Not meeting minimum mailing dimensions.
2. Dark/black background color on mailpieces.
3. Screening and imaging.
4. Return address placements on letters and flats.
5. Text or graphics in the Barcode Clear Zone.
6. Postcard Design.
7. Insert Shift.
8. Folded Self-Mailer Construction
9. Address Placement on Flats
10. Requesting Uniquely Assigned BRM ZIP+4 Code
View 10 MOST COMMON MISTAKES IN MAILPIECE DESIGN notes.pdf