Try this: make a column for each Civil Rights movement you are supposed to include in your poem. Brainstorm words and phrases that pop in your head when you think of these people and events. You don't have to use every phrase or all the words, and some phrases and words you may want to use over and over for effect (repetition).
For example, when I think of Rosa Parks, I think of strong, silent defiance in a front seat. MLKJ to me is peace, equality, spiritual leadership, marches.
Don't discount any idea. Write them all down, and then play around with the words and phrases until you've covered all the requirements of your assignment. You might even look through magazines for words that catch your eye and can be applied to these events/people.
Nothing says it has to rhyme, but arrange the words so there is some "music" to it...it should flow and have a natural rhythm. Think of it as a song. Once you've collected your words and phrases, go back through and see what words you can remove without effecting the value of the sentence or idea you are communicating.
Good Luck, and have fun! This sounds like a great assignment. Check out the links below for more ideas to help you write and polish your poem.
Try this, think of what you want you want to write for your poem, what characters you want to portray in the civil right movement. Try and make a mind-map of these characters, stating its good qualities (using words or phrases) or bad qualities if there is one. Try to flesh out the character, give it a tint of emotion or realism into it, maybe use some literary techniques like personification or metaphor to bring them to life. Try planning out the structure of your poem, how many stanzas, how many lines to fit into the poem. For Martin Luther King case, you can say he is very passionate, a good public speaker, or he is the savior of the world. Brainstorm the qualities of his and other characters you are writing about and jot it down.
Or, are you trying to write a conventional structure like a sonnet or an ode to a character. Language is also very important. it must be vivid and striking and effective in bringing out the main point of the poem, and not being colorless and predictable.
Maybe using some sound techniques like onomatopoeia, assonance or alliteration can help you. Using rhyming words to the best effect. Treat as a smooth-sailing music, just play around with the possible literary techniques and words and let your imagination run wild. Ideas that you never imagine may come up in a nick of time.
Then, just cross out what things you don't want to put into your poem and just jot down your idea of the poem you are going to write about.
Hope it helps. You can produce a draft copy for your teacher to see and review. Your teacher knows best.