Yes Mark is right,
Ken suburi is good as the cutting movements come from and return to centre, but start slowly and keep relaxed and try and keep an awareness of the movements from hara, always turn on centre too, remember that centre is a sphere and you should turn and move in harmony with that sphere to create the spherical movements that will help you develop centre and technique. If you go at it hammer and tongs you will only be unbalanced and loose your cool. Quality is far superior to quantity! Be calm and efficient!