Partition the unobserved variables into two or more subsets, over which the independent factors will be derived.
For a given partition \mathbf{Z}_j, write down the formula for the best approximating distribution q_j^{*}(\mathbf{Z}_j\mid \mathbf{X}) using the basic equation \ln q_j^{*}(\mathbf{Z}_j\mid \mathbf{X}) = \operatorname{E}_{i \neq j} [\ln p(\mathbf{Z}, \mathbf{X})] + \text{constant} .