How should I be planning my reduction print designs? I'm having a hard time planning designs for reduction printing (carving a block for printing, carving more away for each colour). At the moment I draw the basic design on the block, but I keep cutting away bits on the first pass that I want darker on the next layer.

Is there a method people use to make this easier?
If the have a computer drawing program such as Photoshop, gimp or Inkscape you could use those programs layering ability to simulate the different cut and colour "layers" you are looking to achieve.

Each layer would correspond to a cut and color.

Different pen tools could also be used to simulate different cutting tools.

And the zoom feature would allow you to assess the graphic presentation and design quality at various scales. Software scale able thumbnail feature.