Similes and metaphors are two of the most powerful tools in the writer's toolkit when it comes to imagery and describing things. Both create images by comparing two unconnected things: similes describe something as being like something else, while metaphors describe something as if it is something else. Naturally, they are used a lot in poetry, where the writer has limited words to get his message, or vision, across. Metaphors and similes can be used to describe things that would otherwise be difficult to picture, such as feelings and emotions, or simply to put a fresh spin on familiar things.
Decide on the subject of your poem. This is probably the most difficult step if you don't already have a clear idea because the possibilities are endless. Perhaps choose a holiday destination you love, an animal you admire or your partner. Whatever you choose, it has to be something you can picture clearly in your head.
Write a list of similes to describe your subject. Remember, a simile compares the subject to something else using "like" or "as." The comparison should describe something very specific. For example, describe your partner's hair by saying: "Her hair is like silk." This suggests it is soft and lustrous. Write down all the similes that come into your mind. Some won't be used in the final poem, but that doesn't matter. At this stage you are just getting some ideas out.
Write a list of metaphors to describe your subject. Remember, metaphors don't use "like" or "as" to draw the comparison; they simply describe something as if it were something else. For example, describe your partner's eyes by saying, "Her eyes are deep oceans." This might say something about the color, but might also say how you could get lost or drown in them.
Decide on the structure of your poem. There is no set structure for poems using similes and metaphors. They can be long or short; they can rhyme or not; they can have clear stanzas or be written in free verse. A simple starting point is to have three or four stanzas of four lines each.
Arrange your metaphors and similes in the order you want them to appear in your poem. The outline won't read like poetry yet because the metaphors and similes are just separate ideas and not linked together cohesively. Focus on the images and not on specific words or rhymes. Play around with what you have until you are happy with it.
Edit your metaphors and similes to create cohesive, poetic lines. This may involve adding words, or removing them, to create fluency. Take "Her hair is like silk / Her eyes are deep oceans." This is not very poetic, but a few simple edits can make two separate ideas flow together:
Hair like silk frames eyes Oceans holding me with a glance My heart lost in their depths
Again, have fun with the words and the language. Once you are happy with it, give your poem a title and write out your final draft.