A dated copy of the official programme page, a written description of the household's own circumstances and goals, and a record of every communication from any intermediary.
Record what the government said, and when it said it
Hypothetical example: Because this framework is newer than the established visa categories and its published terms can be updated, the single most useful habit is documenting the version relied on. Save or print the official page, note the date and keep it. Write down, in plain language, what the household understands the programme to require, what it costs, who in the family it covers and what happens if plans change; then check each of those statements against the page itself rather than against memory.
Keep the same discipline with third parties: if anyone offers a reservation, a deposit arrangement or an expedited route, record who they are, what they claimed and when, and compare it with the official material before replying. None of this is legal analysis, but it produces a file that a professional can review efficiently, and it prevents the common failure of acting on a version of the programme that no longer exists.