Confirmation button on the left, gray confirmation buttons, green cancel buttons (when the action you are performing is against the website, like subscription cancelation) or red cancel and gray confirmation.
Or hiding CTAs (like adding something to cart) under a hypertext rather than a button.
Different behavior for the same looking content (sometimes it redirects, sometimes it opens a new tab, sometimes it opens a modal).
Resetting forms on error - why the fuck do it need to fill it again?