A good way of writing poetry is to take a poem that you already know and make changes to it.
You may already know this nursery rhyme:
Mary had a little lamb,
Its fleece was white as snow.
And everywhere that Mary went,
The lamb was sure to go.
Here is an alternative version:
Mary had a little lamb,
It played the clarinet.
It also played the violin,
Oh, what a clever pet!
The first line has been kept the same, and the rhythm is the same as in the original verse (DA da DA da DA da DA and so on). The second and fourth lines rhyme with each other (clarinet and pet).
In this activity, you can practise writing your own versions of nursery rhymes.
Have fun!