Pick words with strong emotions IE if the author is talking about Slavery, and she uses words like "abomination" and "sinful" it is apparent she is against slavery, or she could use "productive" and "justifiable" meaning she is in favor of slavery.
Just underline words that stand out to you as emotional, whether positive or negative, and when you're done underlining, go back and read just the words you underlined and decide on the over all "attitude."
(There is no such thing as a list of "key words").
