The Chicago Post Office is offering tips to ensure gifts and greetings arrive on time this year.

The U.S. Postal Service has seen a double-digit increase in package shipments already this holiday season. So postal officials say the earlier customers can mail, the better.

First-class mail should be sent by Dec. 20 to arrive in time for Christmas. The recommended deadline for parcel post is Dec. 14 and for express mail, Dec. 22.

The post office also recommends senders put a card with both the delivery and return addresses inside each box, in case the outer labels fall off or are destroyed.

Customers who don't want to deal with lines can create pre-paid shipping labels using their own PC and printer. Free package pickup is available at no cost.