Always try to use verbs for your affirmative and negative actions. Imagine the button is a normal person (not an engineer) saying exactly what they want to do. Example: [Cancel My Subscription] [No, Keep it]. Make it crystal clear what the buttons mean. Never use OK and Cancel. OK isn’t clear. Besides, the user wants to be sure he/she is pressing the right button.
I often use green checks and red x’s to indicate the positive and negative responses.