Gather the actual notice, application or travel details and relevant correspondence where available. Identify the date, process and stated basis accurately. Work outward from whatever is dated. Start with the passport pages and any admission or refusal stamp, then the application confirmation or receipt number, then correspondence with the post or the agency, then your own contemporaneous notes. Each layer is weaker than the one before it, so label them as what they are rather than folding recollection into the record as though it were documentary.
Separate the record from your recollection
Explain unavailable information honestly and follow the applicable disclosure questions. Do not create a replacement notice or omit the event because the original document is missing. A second file belongs beside the first and is built on a different timetable: the lawful source and path of the capital.
Sale agreements, tax filings, bank statements showing each transfer, loan documents with their security, and gift instruments where relevant all take time to obtain from third parties, and none of them can be produced quickly at the end. Begin requesting them while the refusal record is being retrieved, since the two enquiries run in parallel and neither blocks the other. Where a document simply does not exist — an old account closed, an institution merged — record the attempt made and what was obtained instead.
An explained gap is workable; an unexplained one invites the question at the point where answering it costs the most.