Each campaign is different and your design should be tailored specifically to your brand, target audience, and campaign type, but below are a few tips that can apply to any direct mail postcard design

Utilize the whole postcard:  One common misconception is that half of the back side of a postcard should be left blank for the address.  Many designs even have a line printed down the middle to separate the design from the address.  Often times this line can be problematic as it can interfere with the barcode placement and could end up increasing your postage rate.  Postal regulations only require a 2 inch by 4 inch space to print the address.  Utilize as much of the postcard as you can to communicate your message and brand.

Select the size of your postcard carefully:  Smaller postcards (4.25” x 6”) qualify for lower first class postcard postage rates, but these smaller cards often get overlooked.  Larger post cards stick out in the mail and allow more space to include additional cover and branding. Larger postcards qualify for letter postage rates, allowing them to be sent standard mail, which is comparable to sending smaller postcards first class mail, but will take longer to get delivered.  These larger postcards can be as big as 6.125”x11” while still qualifying for the letter postage rates.  Beware, that certain dimensions cost more to print, cost more to mail, and may not comply with postal regulations, but a mail house can tell you what size postcard will be most cost effect for you to print on.

Clearly display your message:  Ensure that your message is clear and easy to read.  

Make it easy for the customer to act on the offer, by having contact information be highly visible and easy for the recipient to locate.  Including a QR code can help recipients get this information or at least direct their eye to where contact information is located.  If you include your address on the piece be sure that the address is in the top left corner so that USPS machinery does not interpret it as the delivery address.