What should I do to facilitate customs clearance at the time of posting?

Complete the declaration form in detail

To facilitate customs clearance, customs declaration form(s) should be completed in either English or the official language(s) of the destination. Completed customs declaration form should be securely affixed or attached to the outside of the item clearly visible for customs inspection.

Customs declaration for the content(s) of an item should be made in detail as required in the declaration form, including:

Unclear description (e.g. marked as “sample” or without giving a detailed description of the merchandise contained in the item), while false, misleading or incomplete declaration may lead to delay in delivery, seizure or return of the item.
For guidelines on completing customs declaration forms, please visit:
CN22: https://speedpost.hongkongpost.hk/speedpost/info/download.jsf?pid=pos401g
CN23: https://speedpost.hongkongpost.hk/speedpost/info/download.jsf?pid=pos401c#
“Easy PreCustoms” online platform: https://easy-precustoms.hongkongpost.hk/epc/?lang=en.

Attach required document(s)

Senders should be aware of the latest requirement of documents and customs clearance procedures stipulated by customs authorities of the destinations. For details, please refer to the following link to the Appendix on Overseas Post - Service Information by Destination to the Post Office Guide:
https://www.hongkongpost.hk/en/about_us/corp_info/publications/poguide/appendix/index.html.

Do not post prohibited items and comply with the import/export requirements for the posting of restricted items

It is the sender’s responsibility to be clear about the relevant laws and regulations on import and export of the destinations, including whether the item to be posted are classified as prohibited or restricted item and the documents required to be submitted (such as commercial invoice, certificate of origin, health certificate, licence, authorisation for goods subject to quarantine, etc.).  It is suggested that such documents be put in an adhesive transparent envelope and securely fastened to the item, in addition to the customs declaration form affixed.  Customs authority may lawfully withhold and/or impose customs duties/taxes on any postal items under the local legislations of respective countries.  Please refer to the Post Office Guide for details of prohibited and restricted items of respective destinations in the link below:
https://www.hongkongpost.hk/en/about_us/corp_info/publications/poguide/appendix/index.html.