Always, and I mean always grab documentation and keep it forever. I've had people try to not pay me, but had to because of some selfies I had on the job as well as other random documents I forgot to throw away. Now I'm in an L&I situation where the company is telling L&I that my job has zero heavy lifting, and because of that I am now required to go back to work even though working prolonged my injury. I have a LOT of documentation with exact weights of some of my tasks so this will be resolved rather quickly, but had I not, they could have lied and I would have been unable to prove anything beyond giving my word.
Here are my rules for maintaining the upper hand. Keep in nind that sometimes you can't always get away with keeping documents or copies and so on, but do what you can.
1.) Grab pictures of the equipment you work on, including make and model.
2.) Grab an occasional picture/copie of reports, emails, and/or summaries, you've filled out.
3.) Keep the occasional detailed log of what you did for a day.
4.) If something goes wrong, keep copies of ALL documents, and communication. If it's a phone call or 1v1 in person, IMMEDIATELY write down everything you remember in detail, and don't leave anything out.
I may be forgetting some, but I've never fought a company and lost. For what I didn't have, thankfully my memory is sharp enough that I could quote conversations exactly as they happened weeks to months back to really hit the point home.
Please, please at least do a little of each, because what seems like a pointless log, or a harmless text could make the difference in a lawsuit, a dispute, and so on. The companies out there assume you cannot prove anything. Say nothing to them, and prove them wrong if the time comes.