I recently attended a Strategic Content Alliance workshop organised by JISC here in Plymouth, and one of (the many) publications we evaluated during the day is the following guide:

http://www.jisc.ac.uk/media/documents/themes/eresources/sca_audiences_guide_v1-03.pdf

There is also a concise edition of the above document:

http://sca.jiscinvolve.org/files/2009/04/sca_audiences_conciseguide.pdf

All good wishes,

--Maged