Repairing cracked or deteriorated mortar joints involves a few steps:

1. **Remove damaged mortar**: Use a chisel or a mortar rake to carefully remove the old, damaged mortar without damaging the bricks.

2. **Clean the joints**: Brush out any loose debris and clean the joints thoroughly to ensure good adhesion for the new mortar.

3. **Prepare new mortar**: Mix new mortar according to the manufacturer's instructions. You can use a pre-mixed mortar or mix your own using sand, cement, and water.

4. **Repoint the joints**: Fill the cleaned joints with the new mortar using a pointing trowel. Press the mortar firmly into the joints, making sure there are no air pockets.

5. **Shape the joints**: Use a jointing tool or the edge of your trowel to match the profile of the existing joints. This helps blend the repair with the surrounding mortar.

6. **Finish**: Once the mortar has started to set but is still workable, use a brush to lightly remove any excess mortar from the bricks without disturbing the newly filled joints.

7. **Cure the mortar**: Keep the repaired area damp for at least 24 hours to allow the mortar to cure properly.

With these steps, you can effectively repair cracked or deteriorated mortar joints, ensuring the structural integrity and appearance of your brickwork.