Hi, a warm welcome in :)
Page 23 of the STL handbook looks at this - if you search inside the preview on
amazon.co.uk use the keyword 'communicating'
The criteria is based on your school's actual practices so maybe consider what literature they use eg. prospectus, pamphlets, leaflets, mailings, newsletters and what the school's website says.
You're looking for information that promotes how the school places their children at the centre of everything, how it works together - internally and with parents, carers, what attitudes are expected, community cohesion, links and how inclusive the environment is.
Hope this helps xx