There are a number of occasions when betting on corners can be a good idea. These can include:
When you have noticed that a team usually wins more corners during a particular period of the match.
If you are live-betting and the two teams you are playing are of similar strength but one team is winning. In this instance the loosing team usually always picks up a higher number of corners.
If you see something in a match that you feel is likely to lead to a corner being won. Perhaps its a wet pitch and the keeper is struggling to control shots at goal.