Answer:
Firstly you should include your layout features (Addresses, date, Dear Sir/Madam etc.). Make sure to leave a space between each one!
Then you should begin with an introductory paragraph. You may wish to use the common 'I am writing to you...' but avoiding this and using something more original may earn you more marks. You could use an anecdote related to your topic, maybe describing an overcrowded prison, for example.
After that paragraph, you should move on to explaining your point of view and eventually your example of alternative provision (if you have one).
Sorry this couldn't be as detailed as I would like but best of luck with the question. :)