A photo proves only what is visible in it. Shoot backwards from that.
Most evidence people collect is almost useful. A photo of a leak with no way to tell whose house it is. A recording of a promise with no way to tell who was speaking or when.
There is one idea underneath all of this:
A document proves only what it shows.
So before you capture anything, finish this sentence: "This needs to prove that ______." Then capture the thing that proves it, not the thing that upset you.
Know what you are proving. "The dashboard warning came on again" needs the warning and something that identifies the car as yours. Two separate facts, and a photo of just the warning light proves neither.
Check what you are allowed to record. In some states you may record a conversation you are part of without telling anyone. In others, everyone has to agree. Getting this wrong can be a crime, and it can make the recording unusable — losing the very thing you were trying to keep. Check your own state before you press record, not after.
Wide, then close. One shot that shows where you are. Then one that shows the detail. A close-up alone is unanchored.
Get the thing that ties it to you. The VIN plate. The house number. The name badge. The invoice header with your address. One frame with the identifier in it is worth more than twenty without.
Say what you are seeing, out loud, while recording. The date, where you are, what is happening. A person narrating in real time is a much stronger record than the same person remembering later.
Photograph the envelope, not just the letter. For anything with a deadline, when it arrived can matter more than the date printed on it. Photograph the postmark next to the document.
More frames, not fewer. Storage is free. The shot you did not take is the one you will need.
Do not edit the original. Ever. No cropping, no brightening, no "enhancing." Make a copy and mark up the copy. An edited original is an original you have damaged.
Do not rename or move files. The file's own hidden data — when it was taken, sometimes where — is part of the evidence. Copying into some apps strips it. When in doubt, keep the file exactly where the camera put it and back up the whole folder.
Write it down the same day. A short dated note: what happened, who said what, what you did. Same-day notes carry weight that memory does not.
Capture their words, not your summary of their words. "He said it would be two to three weeks" is evidence. "He kept stalling" is your conclusion, and it can be argued with. Quote them. Let the quote do the work.
After anything happens, take sixty seconds and ask: if I had to show a stranger that this happened, what would I hand them?
Then go get that, while you still can.