Action Details
Requirements and how-to articles for Google My Business's action:

Write a post which provides general information about your business, such as new products/services.

You need this to get it done:

Write your post, including relevant information about your business and/or product(s) (maximum of 1500 characters.)
Photos should be simple, direct, in-focus and well-lit, with bright, vibrant colours.
File format: .jpg/.png
Minimum resolution: 400 x 300 pixels
Note: You can use either a photo or a video, but not both.
File format: .avi/.mp4/.mov/.flv/.wmv/.mpg/.m4v/.mkv/.m2ts/.mts
Maximum file size: 100MB
Note: You can use either a video or a photo, but not both.
Call-to-Action Button
The following calls-to-action are available with "What's New" posts: "Book", "Order online", "Buy", "Learn more", "Sign up", "Call now"
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Google My Business Help - Post on Google
Official guide to making business posts on Google.
Link missing here or found errors? Improve How-Tos