Here's another tip/trick.
Let's say you have an engine or car that derails. This could turn out to be a good thing. In fact, it could be an opportunity to improve your layout.
How could that be?
Try your best to figure out why the derailment is happening. If the derailment occurs in one place on your layout, look closely at your trackwork in that spot and consider using a shim to make the track more level or adjust it in some way.
I recently did the above with my recently acquired 18 inch passenger cars (which are long for the 031 curves on my layout). After I adjusted the track with a shim, the derailments stopped, and my trackwork has improved.
