What are some good/best ways to annotate essays?

For rhetorical device essays:

-note any times figurative language is used--and explain its purpose in the work as a whole

-analyze the syntax and diction of the passage - - ex: its affect on the tone.

-underline anything that stands out to you

For synthesis:

-determine the tone or what side the author is on (pro, con, qualify)

-underline whatever stands out and explain why it does.