Hmm, good question. I usually use the default directory structure / layout for Rails applications. As for architectural things, I typically stick with monolith apps as they're faster to develop and easier to debug. Over time, it's good to extract some things in to services where it makes sense.
One thing we do at work that I think most Rails apps may not do is that we don't allow the use of instance variables in views. I like this because in a view, it's hard to tell when an ivar gets initialized and what order its done. An ivar in a view is basically a global variable and comes with all the pitfalls of globals.
I hope this helps!