Concise Guide to Researching Audiences
Here is some useful guidance developed by the JISC Strategic Content Alliance.
http://sca.jiscinvolve.org/wp/audience-publications/
The best place to start is the Concise Guide to Researching Audiences http://sca.jiscinvolve.org/wp/files/2009/12/sca_audanalysis_conciseguidetoaudresearch_v3-final.pdf