At to top of the screen next to the Magnet icon for "Make Live" are two arrow icons. The left one shows a list of inputs, the right outputs. Inputs shows deformation and other things. Left click on it and pick the last item: All Inputs.

This brings a list of all the affecting input calculations, such as the binding of the skeleton (skin clusters) and the blend shape. Middle click and drag on one of them down below or above another to make it calculate before or after the others.

The order of deformation is the order that Maya calculates somthing. For example, you want it to calculate the blend shape first, and THEN the skeleton binding so that the result of the blend shape will be affected by the skeleton.

If you make a blend shape after binding, it automatically becomes the latest and thus last calculation, so when you rotate the neck and then blend the face to a new facial expression for example, the head will morph back to its original position rather than taking the skeleton into account.

Hope that makes sense.