Obviously, you need to know enough about Jefferson to "get into his mind" and not only write in his style, but write as he would think. Do you know that much about him. If not, then you need to do some reading.
The first four links in here are to pieces of writing of Jefferson's:
And of course -- the Declaration of Independence:
Once you are immersed in his writing and thinking, then you'll be ready to choose someone in our country or world today about whom Jefferson would have had an opinion. Then plan and write.