Non-negotiable
Avoid text spilling out of containers Avoid element collisions at awkward responsive sizes Avoid pixelated/stretched images Use SVG for icons and vector graphics
Default
Ensure that webkit font smoothing is set to "antialiased", but not for reversed text Ensure consistency between colors used. Try not to use close but non-matching colors Ensure that retina screens receive higher-res imagery Ensure that hover and touch "down" states are present. Should be simple and helpful. Create smooth, simple transitions for animating elements
Advanced
Extreme
Add custom shadows to modify font hinting for particular cases