There is a sticky up above on how to do this, but it is a long thread to read through. You want it to arrive the day before you do (or the same day). The resort obviously can't store packages long-term. UPS, DHL or FedEx is fastest because regular US mail (Priority Mail, etc.) may have to be sorted at a central facility (with an estimated two-day lag) before being sent to the resort. It is best to purchase the "signature required upon delivery" add-on for verification and tracking purposes in case the package goes missing after delivery.
If you are staying at one of the so-called convention resorts, you may have to pay a fee for package retrieval ($5 and up depending on size) and may have to go to the convention center at the resort to pick up the package. There are different accounts for other resorts as to whether the package will be sent to your room or waiting for you in a storage room near the front desk.
You want to address the package to yourself at the resort. Include arrival date and reservation number. Here is one example of how to do it:
Your Name (guest; arriving Jan. 15)
Reservation #123456789012
c/o Disney's Wilderness Lodge Front Desk
901 Timberline Drive
Lake Buena Vista, FL 93830
Some say to put your name and arrival date on various faces of the box, but that isn't essential and obviously can't be arranged if you are shipping from the
Disney Store. Good luck!