Keep cards simple
Cards are meant to just show a taste of the available information. Don't overload cards with more information than necessary.
Don't add buttons to quiet cards
Only standard cards can have a footer, and buttons can only appear inside a footer.
Don't align individual cards to the column grid
Individual cards are not aligned to individual columns in the page's responsive column grid. Instead, groups of cards are aligned to the column grid in a layout region.
Don't auto-play videos
If the preview is a video clip or other moving item, do not automatically play the clip or motion. Save the movement for either when a user hovers on the card or when they click on a play button.