Does reading a book out loud make you better in social situations? Suppose a person reads a book out loud for 1 hour straight. Would this "exercise" the parts of the brain involved in speech? Would this make the person a better communicator in social situations?
Based on general principles of skill transfer:


Reading a book aloud should improve your skills in reading books aloud, and in particular it should improve your skill in reading the particular passages that you are reading. So if you are going to be reading a particular text in a public setting, it makes sense to practice reading that passage of text.
Likewise, if you are preparing to give a lecture, then practicing giving the lecture should improve your performance giving that talk.
Reading a book aloud is unlikely to help you in social situations because the dynamics of reading are quite different to the dynamics of social situations. Communication in social situations is interactive with its own specific set of conventions that need to be learnt. In contrast, reading a book aloud is not interactive. The rules that govern reading a book aloud are very different to those that govern social situations.


Based on the same principles, if you want to be a better communicator in social situations, your time would probably be better spent (a) studying social interactions, and (b) engaging and reflecting on social interactions.

Update: @ofri makes a good point. If a bottle neck on your social skills is actually articulating words clearly, then practicing that skill, such as would occur when reading, should be effective. Ofri uses a good example of a second language learner. The case I'm thinking of above is where the person is fully competent in articulating words verbally, and where problems with social skills relate more to knowing what to say when.