Mad Libs are a great way to play around with voice and have fun at the same time.
Before you begin there are a few rules.
1) Your voice is controlled by the kind of Mad Lib you are playing.
So if you play Hamlet's third soliloquiy, use words like Shakespeare
would. Act like a physics teacher for Art Hobson's Mad Lib. Pretend
you are the Beatles. You get the idea -- play a role.
2) Your role requires you to relate verbs as the persona your
role suggests would say
3) Nouns are modified by the kind of person you project yourself
as
4) Adjectives and adverbs are regulated by the nouns and verbs
your role chooses
The result, the story you create in your Mad Lib, is your voice in that role. Think of an essay in such a way, and your voice will come out easier.