Care is needed to avoid over-cutting as this will cause bleeding. This can be stopped using a silver nitrate pencil - but often the bird rubs it and bleeding starts again. For this reason beak trimming is best performed by a veterinarian.
Moving the bird into a larger cage may help increase exercise and so increase natural wear of the beak. Contrary to popular belief cuttle bone and mineral blocks are not thought to help with beak growth.
The underlying cause (eg mites) should be treated appropriately. See cnemidocoptes pilae.
Long term problems
Updated January 2016