One thing that could be considered is the various potential users: eg members of the society, potential members, and general visitors interested in the society. The general welcome page might have subpages for each type of visitor containing the most useful information for them.
It might make sense to organise membership renewals through the site (if this could save the society money, for example).
Up to date information on the society’s activities: grants awarded, visitors funded, conferences, and so on is very useful. A list of books published by/through the society would be great (or could be a link to publishers’ pages, perhaps making it easy to get the LMS discount).
It’s vital that updating it is easy and there are no problems with permissions for those updating it. Some systems seem to involve complex overlays of html and take a long time to edit and then get replaced a few years’ later leaving many useless pages that have to be rewritten. Using direct html has some advantages!
Comment by Robert Marsh [converted to a post]