The great thing about freestyle (free verse) poetry is that it frees the writer from having to focus on meter and rhyme. That isn't to say those elements aren't present in freestyle poems. As the name implies, anything is possible when you're writing a freestyle poem. If you are accustomed to working in a structure you may find freestyle more challenging, but for those who are new to poetry writing freestyle can be a liberating way to get into poetic expression.
Brainstorm for topic ideas. A poem can tell a story or simply relate emotions. With a freestyle poem, you have more opportunity for story telling because the confines of rhyme and meter are not present, which allows you to be more open with the length and structure of your poetry lines.
Consult a thesaurus to find unusual or different words than the ordinary for what you want to say. Since you won't be getting readers' attention with creative rhymes (although you can rhyme if you choose), you need to reel them in with the beauty of your language and the originality of the story your poem tells.
Structure your freestyle poem according to content. Although freestyle requires no specific structure, the content of a poem can dictate a structure. If your story has many facets, separate them into stanzas, with each stanza telling a standalone part of the story. If you have a short poem that follows one train of thought, avoid the traditional stanzas and write one block of text.
Experiment with visual elements if they can help bring the message of your poetry out more clearly. One example of visual experimentation is to write a word with every other letter capitalized to illustrate the ups and downs of an emotional character. Excessive use of the ellipsis indicates broken thoughts or uncertainty.
Write with the devices used in other poetic forms. Metaphors, similes and other literary devices bring out the message of your poem. Again, since this is free verse you aren't required to use figurative language, but these devices give readers something to zero in on if your poem lacks a rhyme scheme or metered verses.