When I work on a responsive interface, I want every decision to make sense beyond just fitting content on screen. It is not only about making things smaller, but about preserving hierarchy, readability and interaction across mobile, tablet and desktop.
I usually start by reviewing structure, spacing, typography and realistic breakpoints. In many cases the issue is not a single component, but the way several pieces interact when the available width changes for real.
I also pay a lot of attention to long titles, buttons, cards and metadata blocks. Those are often the elements that break layouts in production if they are not designed with enough frontend margin and intention.