Every published protocol on documenting these crimes opens with the same principle, and it is not a formality.
The person who gives you an account can be killed for it. Names, faces, locations, vehicle plates, the fact that somebody spoke to you at all. A record that identifies a witness in occupied or contested territory is a record that can be used against them by whoever finds it.
Ask before you record a person. Explain who you are, what the material may be used for, who may eventually see it, and that you cannot promise it will never be seen. Consent given without that is not consent.
Do not re-interview a traumatised person for a better version. Repeated accounts of the same trauma damage the person and damage the evidence: inconsistencies introduced by re-telling are used to discredit them later.
Do not promise what you cannot deliver. Not prosecution, not compensation, not protection, not that anybody will ever be held to account.
Do not collect what you cannot protect. Material on an unencrypted phone at a checkpoint is material in somebody else's hands. If you cannot secure it, consider whether you should hold it at all.
Sources. UN Office of the High Commissioner for Human Rights, Berkeley Protocol on Digital Open Source Investigations, https://www.ohchr.org/ ; OHCHR, Minnesota Protocol on the Investigation of Potentially Unlawful Death, https://www.ohchr.org/sites/default/files/Documents/Publications/MinnesotaProtocol.pdf ; Eurojust and the Genocide Network guidelines.