Annotation is very personal in that it is the reader's transaction with the text. Each reader will come to a text with his/her own life experiences and background knowledge, for that reason, each reader will want to highlight a different aspect of the text. As a general rule for those beginning to use annotation, you may want to underline/highlight interesting words/phrases. You may want to circle unknown vocabularly. You may want to question what the text means by writing a note in the margins, or you may use marginal notes to jot down ideas you have about meaning, or literary elements. In the reference links, I am linking an article by Dr. Robert Adler, about how to mark a book.
Regarding Sonia Sanchez's poem, it is best to begin one stanza at a time. (Annotations will be bolded)
Our vision is our voice --Alliteration. Their goal is their guide.
we cut through the country
where madmen goose step in tune to Guernica. --Guernica was bombed during the Spanish Civil War in the 1930s.
we are people made o fire
we walk with ceremonial breaths
we have condemned talking mouths. -Condemned talking mouths? They don't want to hear other's voices? Mouths - Guernica -- perhaps referring to the Pablo Picasso painting?
we run without legs
we see without eyes
loud laughter breaks over our heads. -Must be the Picasso painting, it fits the image. This is an ekphrastic poem, then.
This is a sample of how to annotate, but as stated earlier, it is best to do this with your own voice, because only you will be able to interpret what you know; however, I hope this will help guide you in the direction you should be looking. (Second link is to an image of Picasso's painting of Guernica.)