To make straight joints, tape should be cut to the correct length. The line where the ceiling meets the wall will need to be taped unless coving is going to be fixed. A trowel of filling knife is then used to put jointing material on the depression of the tapered edge board. The tape then needs to pushed firmly into the filler with the trowel/filling knife. So that no air bubbles are left, the air needs to be forced out and there should be 1mm or less of filler under the tape. If the tape is not pressed in properly, it will blister and the tape will then need to be removed and replaced. The tape should then be covered with joint filler making it level with the board. Once that coat has dried, another two coats of filler should be applied so that three coats have been applied altogether. Make sure you have allowed time for each coat to dry in between. To get a smooth finish, each joint should be sanded down. If you sand too much, the paper tape will become rough.
If there are any nail or screw holes, they will need to be filled in with the same amount of coats as the joints.