Generally a brief note or a phone call will suffice.
通常写个便条或打个电话就足够了。
《牛津词典》
2
Other choices, in descending order of personalization, are: a real-time phone call, a voice-mail message, a handwritten note, a typewritten letter, and the most unfriendly is email.
A thank-you note or telephone call after the visit is also considered polite and is an appropriate way to express your appreciation for the invitation.