Preventing scratches on iPhone X absolutely is a difficult task because of the stupid stainless steel border. Normally, screen protectors and a case with good material and design would do.
For iPhone X, the weakness link is the border. The way the stainless steel is used on iPhone X is unreasonable from scratch resistance standpoint. It is not the same as say, 10 year old iPhone 3GS where the stainless steel or chrome border is only half-width. Even the SIM tray cover is made of shiny metallic like material increases the chance of scratches/dents in the area over time.
Out of the box, if you use strong bright white LED to inspect it, you will find imperfection because I did. Stainless steel is strong but is extremely prone to marring. If brushed stainless steel, it would have been a bit better.
So in case of iPhone X, having a case is an absolute must. To be more critical, it is best to find case with only soft TPU in direct contact of iPhone X. You can get two-pieces or multiple pieces case but the main point is TPU or leather or silicone should be the medium which is in direct contact with the stainless steel border. Besides, I would avoid choosing cases which are tight fit because putting the iPhone X in and out of the phone case would abrade the stainless steel border if the material is too hard.
There is one other solution -- putting a skin that covers the stainless steel/space grey stainless steel border of iPhone X in addition to a case.