There are plenty of existing memoirs, letters and diaries that would give you an idea of how someone in the period might write. The Memoirs of Sir John Clerk of Penicuik and the Memoirs of the Life of Colonel Hutchinson are over on the Internet Archive. But a very readable source of style that would be easy to find would be John Auibrey's Brief Lives . Aubrey was a curious man and good at collecting and noting stray bits of information, but not very good at organizing it, so a huge pile of biographical notes he prepared for doing a 17th c. version of Plutarch's Brief Lives stayed in a pile long after he died, and so give an uncensored and unpolished example of how someone might write before publication. There are numerous editions to choose from. Froude's early attempt from the 19th c. is at Project Gutenberg and will work, but it's more like looking through the pile, note by note. The Oliver Lawson Dick edition attempts to finish Aubrey's book- it's been out for a long time and so is very common. The more recent John Buchanan-Brown is more scholarly, but rather scarce.