Writing Poems by "Talking Back"
One of the best ways to learn how to construct a simple poem is to take someone else's poem and use it as your structure. This is not cheating or copying, because you write your own version with your own ideas. For example your students could write their own poems based on William Carlos Williams' poem The Red Wheelbarrow, but instead write about a topic of their choice. They use Willams' simple one or two word lines as a starting point.
For a whole book on this topic, try Talking Back to Poems by Daniel Alderson. It has lots of examples and poems to use.

A haiku is a three-line poem with a total of 17 syllables (5/7/5). There are websites such as this that explain how to write a haiku and give a number of examples.

Along with haikus, your students can then go on to write cinquains and tankas. These are all simple short poems with some rules to make it more fun!

First Lines/Last Lines
Give your students several first and last lines to choose from, then ask them to write a poem using the lines they have picked. If you like, you can use lines from published poems, or make up your own, or use mine:
First Line
This was not the day
Beneath the bridge
The photos on the piano
Music filled
In the small town, on the widest street
In the mirror
You must not call me

Last Line
and the sound went on.
you ended with nothing.
painted on the wall.
like the black night.
too many flies in the soup.
only you will know the answer.
in the box.

There are many ways to use repetition in a poem:
1. Choose one word (e.g. nose, which can also be knows or nos) and use it at least ten times. It's good to use a word that sounds the same but is spelled differently and has different meanings.
2. Repeat the same word or words at the beginning of each line. E.g. Someday I will, Can you hear, You will be, When I am - these are simple ones.
3. Write a line that can act as a refrain, then use it three or four times throughout the poem.

Write a poem in which you compare two opposite things (such as rocks and water, or smile and frown), or a poem about two completely different things (such as car and cloud, or tennis ball and snail). It's often better to use concrete objects or actions rather than emotions or abstract concepts such as honesty or courage.