How do I design Rails apps for better performance and conversion?

I’m working on several Rails-based products where the backend is solid, but I’ve noticed performance and user flow issues impacting real user behavior (drop-offs, slow interactions, low engagement).

I’m curious how experienced Rails developers approach:

Structuring controllers/services to keep response times predictable

Handling caching (fragment vs. HTTP vs. background preloading) in real projects

Improving perceived performance in Rails apps beyond just server speed

Any patterns you follow to keep UX and backend logic aligned

Not looking for “one right answer” — more interested in practical approaches you’ve seen work in production.
Appreciate any insights or examples from real projects.