Go through the word mat with your child and read the words with them.
Help your child construct their first sentence as some children find it hard to get going.
Encourage them to say their sentences aloud before writing and using their phonics to help them spell.
Your child should manage to write the whole story using some adjectives , conjunctions and sentence openings. Don't worry if spelling is not perfect but they should be making sensible and plausible attempts at words. There should be a clear beginning , middle and ending.
Ask your child to read their work to you.