When I first began optimizing websites nearly 20 years ago, the meta description was one of the most influential elements in the positioning of websites on the search results.
The description attribute within the meta tag provided a way to show a summary of each page's content in a well thought out and optimized manner. The problem today, however, is that search engines (Google in particular) doesn't always use the meta description provided by the page within the snippets found on its search results.
As it stands today, Google will only use the meta description provided by the website if it believes that it provides a better (more accurate) description than what is available purely from the on-page content.
Since meta descriptions can improve click-through rates from the search results, it is essential that search engine optimization professionals know all they can about how meta attributes work and what they can and can not do to improve performance of this vital website attribute.
Consistent Presence: While no one really knows if Google penalizes for duplicate meta descriptions any more, if you're focusing on the user (as you should be) then it is important to ensure that each meta description is unique. That could be incredibly challenging but Search Console actually provides data to help webmasters identify missing or problematic descriptions on their websites (available on the HTML suggestions page in Search Console).
Uniqueness: Google is less likely to display the meta description if it has determined that there are identical or similar descriptions on similar pages of a website. Creating unique descriptions for each page ensures that the work put into customization of this attribute pays off for the website and helps avoid having Google return what it believes is an appropriate description of the page.
Clarity & Creativity: Most search engine optimization professionals follow a rather traditional approach to the development of this attribute, employing the sentence form. But remember, description are used to attract visitors, so why not make the use of this virtual real estate? Consider thinking outside the box and including product prices, a list of benefits that don't include your primary keywords, perhaps even a clever quote.
Another important note related to meta descriptions is that it is of fundamental importance to have a process and procedure in place for the development of these attributes. Most content management systems and e-commerce platforms either provide the ability at their core or through plugins or modules to help webmasters optimize (or at least include) the meta description attribute, but they won't develop them automatically. Knowing how your specific software system handles and manages the attributes will lead to greater SEO performance in the long run as you won't be spending time recreating those elements after the page has been published.
What's your best advice for making the most of the meta description attribute?