There is extensive web-based guidance for caseworkers under the points-based system, much of it linked from: https://www.gov.uk/government/collections/working-in-the-uk-modernised-guidance

Guidance for sponsors is on a separate link from the UKVI page. Click on Sponsors, which takes you to: https://www.gov.uk/government/collections/sponsorship-information-for-employers-and-educators

You can also read about the work of the Migration Advisory Committee, and read the minutes of their meetings, at https://www.gov.uk/government/organisations/migration-advisory-committee.