Rob,
The painting techniques don't vary greatly between sizes of figures, although obviously the larger sized figures should be more detailed and smaller details are more visible to the naked eye. The only significant difference would be the size of brush you use, otherwise the painting processes are more or less identical.
The major difference in the way you paint larger scale figures over smaller scale figures is the use of contrast between the extreme highlights and shadows.
The general rule of thumb is that the level of contrast increases as the size of the figure decreases. The same is true in reverse. As the size of the figure increases, the amount of contrast required decreases.
It's hard to explain, but it makes sense when you see it.
Small scale figures (28mm up to 54mm) require a relatively high level of contrast to emphasise the light and shadow effects. When painting in larger scales like 1/10th scale up to 1/6th scale, you need much less contrast.