1. Enclose items in plastic bags and keep them off the floor
You should also store them low in the house, as heat rises. Storing valuables in an attic is not a good idea, as firefighters typically ventilate the attic trying to push the fire inside the house up through the roof. This means heat in an attic will be intense as they ventilate the fire.
2. Valuable one-of-a-kind items should be stored in a fireproof safe
However, this can be a problem if you want to display them.
3. Important documents and photos can all be duplicated now with relative ease
There are amazing digital scanners that can scan stacks of paper in just seconds per sheet. Dedicate just 20 minutes each day until you're finished to go through all your things. Once complete, you'll have a digital copy of everything that's of value to you. The trick is to put that digital content on multiple external hard drives and store them at friends' or relatives' houses. You don't want those hard drives in your home, where a fire can consume them as well as the originals.
4. Take videos of all of your possessions twice a year
Scan receipts of all things you purchase. You'll need these records (save them off-site) to prove to an insurance company that you owned all the things you have. Imagine how hard that could be without receipts, as you're talking, in shock, with an insurance adjuster while you both stare at a pile of smoldering ash and cinders.