How do you attach curtain brackets to a drywall?

The best way is to find a stud in the wall and use screws. If your place of choice is not near a stud, then you simply use EZ Anchors. These are large thread hollow screws made in 4 sizes and in plastic or aluminium. They have a triple point for biting into drywall and are screwed in with a Phillips or Pozidrive screwdriver, When they are in, they fit flush to the wall and you can the insert a woodscrew or drywall screw and hang almost anything from them I have used 6 of these with L brackets for a bookshelf that holds over 100 pounds of books. Look in Home Depot screw section, they have these in 4 sizes, in packets of 4, 20 and 100. -Once you use these you will never use any other way.