Measure the area where you want to place the bracket with a tape measure. Ensure that the bracket will fit into these dimensions.
Take the bracket and place it over the location. Make marks at the corners with a pencil.
Drill holes at the manufacturer's recommended spots on the bracket to hold the screws. Dispense with this if the bracket comes with pre-drilled holes.
Mark the location where the screws will enter the siding or fascia. Drill holes slightly smaller than the screw size at these marks.
Center the bracket over the marks on the house. Ensure that the holes for the screws on both the bracket and the house align. Check that the bracket is plumb and level with a carpenter's square.
Fasten each screw into the house with the drill.
Countersink the screws, if you do not want them to remain visible. Cover the holes on the brackets left by countersinking the screws with wood filler. Use sandpaper to smooth out the material to the level of the surrounding surface of the bracket. Paint to match the bracket color.