An external angle dry lining bead can be used for showing angles. For unexposed angles, you can use a special paper tape that has two metal strips on it.
On each side of the angle, you should apply jointing material 50mm wide making sure that they are well covered. The quality of the angle will be affected if not enough material is used because it will bubble up. Tape can then be placed into the angle after being bent 90 degrees, making sure that the tape is pushed into the jointing material. The tape should then be covered in a coat of jointing filler. Once this coat has dried, apply another two coats making sure you leave time in between each one for it to dry. The joints can then be sanded down to get a smooth end result.