Will the reader understand what you want them to do?
Have you included all the necessary information in the task?
Is it the recommended word length?
Does each paragraph have one sentence that describes the main idea? Do the other sentences give more information about that idea?
Are there paragraphs?
Does each paragraph have only one main idea?
Are the paragraphs in a logical order?
Are your sentences too long? Two shorter, simpler sentences are better than one long one.
Can you say it in a simpler way?
Do you repeat the same words? Use different words that mean the same thing.
Have you checked that nouns and verbs agree?
Have you checked that you have used the right article (a/an/the/-)?
Have you checked that you have used the right tense?
Have you checked that spelling and punctuation are correct (. , ; : “” ' )?
Is it polite?
Is your writing the right tone for the person you are writing to?
What is your relationship with the person you are writing to? Do you know this person well or not?