Well, you can probably start with blacklining and edge highlights rather than any gradual shading done with washes/drybrushing/airbrushing. Emphasize contours with strong, dark lines.
Here's my old method of painting Tau (Pathfinder conversions in this case):
The model was painted black, then grey was painted on each panel, effectively giving it a blacklining effect without actually doing blacklining. Edges of plates got highlights, and edges of cloth got highlights - there's only shading going on on the orange of the antennae, but it's not gradual at all, it's bands of colors. This Tyranid by Nard shows a similar technique, as is closest to what I'd call 'cell shaded':