Now I see why my previous attempts to model in Blender didn’t succeed – my reference images were not level and not the same scale. Whilst there was nothing mentioned on the tutorials at Blender Cookie (in those tutorials, the reference images came already prepared), the first step that Angela Guenette (modeller on the Sintel short – cover on the right) on the Blenderella DVD immediately mentioned is to prepare the reference images in GIMP: rotating, scaling, and adding horizontal reference lines to allow you to line up features across the various reference images.
Wish I’d known about this before spending time on my last modelling attempt. :/
Oh, well, you learn from mistakes.