"Pay attention and don't talk."
Translation:Dávej pozor a nemluv.
Dej or Dejte is more of a 'watch out'. Once and done Perfect aspect of verb. You are about to walk off a curb and somebody tells you to watch out, watch the step.
Dávejte or Dávej is a continuous attention. Something you would say to a child in school. It makes more sense with the "do not talk" part.