After a fire, a flood or a burglary, the insurer asks for a list of everything you owned. Most people find out at that moment that they cannot remember half of it, and cannot prove what they paid for the rest.
The claim is only as good as the list
Adjusters work from what you can show them. A television you can describe is worth something. A television you photographed, with the receipt, the model number and the date you bought it, is worth what you actually paid. Across a whole house, the gap between those two adds up fast.
Go room by room
It sounds obvious, but it is the difference between finishing and giving up halfway. Walk into one room, photograph everything in it, move on to the next. It is also how a claim gets read, so a list organised by room is easier for an insurer to check.
Keep the paperwork with the item
Receipts and warranties are your proof of value, and they are the first things lost in exactly the events you are insuring against. A photo of the receipt stored next to the item it belongs to survives when the shoebox does not.
Keep a copy somewhere else
An inventory stored only inside the house has the same weakness as the receipts. Export it, date it, and send a copy to your broker or leave one with a relative.
HomeStock is an Android app that builds that inventory room by room, with a photo, a value, the receipt and the warranty against each item, and exports the lot as a dated PDF. Nothing leaves your phone until you choose to send it.