Learn responsive design by building, not reading. Start with CSS fundamentals: flexbox for one-dimensional layouts, grid for two-dimensional structures, and media queries to adapt styles at breakpoints. Mozilla Developer Network (MDN) has the best technical documentation—skip video courses that pad runtime. Adopt mobile-first methodology from day one. Write base styles for small screens, then use min-width media queries to enhance for tablets and desktops. This forces you to prioritize content and prevents desktop assumptions from bloating your mobile code. Most traffic comes from phones now, so designing for 375px-wide viewports first isn't academic—it's practical. Pick three real websites you visit daily and rebuild their layouts from scratch. Don't copy-paste their code. Inspect elements to understand their approach, then close DevTools and implement your own solution. You'll hit problems with navigation menus, image scaling, and typography that no tutorial covers. Solving these yourself builds intuition that watching someone else code never will. Test on actual devices, not just browser DevTools. Chrome's device emulation misses real rendering quirks—Safari on iPhone handles viewport units differently than Chrome's simulator suggests. If you can't afford multiple devices, use BrowserStack's free tier or test at an Apple Store. At Ottawa SEO, we caught a client's mobile nav breaking only on physical iPhones because click events behaved differently than desktop hover states. Key techniques to practice: fluid typography with clamp(), container queries for component-based layouts, aspect-ratio for responsive media, and srcset/picture elements for performance. Learn to optimize images—a 4MB hero image kills mobile experience regardless of how elegant your CSS is. Spend 20 hours building before spending 2 hours reading about best practices. Responsive design is motor skill development. Your fingers need to know how to structure HTML that flexes naturally before your brain can architect complex systems. Most developers plateau because they consume content instead of shipping broken prototypes and fixing them.