It can be intimidating to send a letter to a country where the Roman alphabet is not used, but rest assured, postmen almost everywhere in the world are used to it. Shanghai is a major cosmopolitan centre, and you will need to do very little out of the ordinary to make sure your letter arrives. With a correct address and postage, there's very little to worry about.
Verify that the address you're using is correct and that your letter meets customs requirements. If you want to include anything other than a printed letter, check with the U.S. Postal Service's conditions for mailing larger objects.
Write the address in the following format:
House number, street name, city
People's Republic of China
In general, the postcode for Shanghai is 200000, although the city has several codes.
Affix the correct postage. To see what the accurate international postage is for the Postal Service, use the international postage calculator available at usps.gov. USPS also provides "Airmail" stickers you can affix with the stamp to make sure the letter makes it on the plane. It should take about a week for your letter to arrive going with first-class international postage.
If you are mailing something important, consider using a couriered service like FedEx or UPS.
Mail entering China is censored and material deemed politically or culturally objectionable may be confiscated.