I'd suggest going skimming through first with a few highlighters, colour coding so one colour's for metaphors, another's for key quotes, etc, with whatever you want. You can also just go through with one colour, highlighting different language techniques. Really just highlight whatever u want to get out of the text.
Once that's done, read the parts you've highlighted more thoroughly and make notes in the margins with a pen/pencil. Comment on structure and language, that kinda stuff. After u do one thorough reading, skim through again really quick and make any other notes u want to.
I think that's about it! hope this helped!