think about the good case first:

Overpair... is it 2 suited? 2 connected? or 3 suited/connected?
how likely is the straight holding / straight draw holding?

bet accordingly. You should generally not bet less than half a pot, and usually bet 3/4 pot, and bet pot if there are 4+ players.

now the overcard miss case or the big pair overcard case:

what are you trying to represent?

how much would you bet if you had what you're representing?

bet that much