You could look at this problem from the p.o.v. of vectors. Vector L points from the origin to the electron-cloud. Vector S’s origin is in the electron-cloud to where L points. If S points in the same direction as L, then the sum of the two vectors will be largest. If S points parallel to L but towards the origin of L, then the resulting vector sum will be smallest. If S points perpendicular to L, then the vector sum’s value will lay between the previous two situations.
-J=2 corresponds to L and S being oriented parallel and in the same direction.
-J=1 corresponds to L and S being perpendicular to each other.
-J=0 corresponds to L and S being oriented parallet and in opposite direction.