Pick the format by content
- JPEG — photographs. Quality 60–80 is the sweet spot; above 85 the file grows fast for no visible gain.
- PNG-24 — anything needing transparency, and flat graphics with hard edges. Terrible for photos.
- WebP — roughly 25–35% smaller than JPEG at matching quality, with transparency support. Safe to default to now.
- SVG — logos and icons, if the artwork is vector. Infinitely scalable and usually tiny.
Why exports look washed out
This is almost always a colour profile problem. The document is in Adobe RGB or ProPhoto, the browser assumes sRGB, and every colour shifts. Convert to sRGB before exporting (Edit → Convert to Profile) and tick Embed Colour Profile in the export dialog. Fixing this one thing solves the great majority of "my colours changed" reports.
Resize, then sharpen
Downsizing softens an image because detail is being thrown away, so sharpening must come after the resize. Sharpen at full size and you sharpen detail that will not survive.
For output sharpening, add a stamped layer (Ctrl/Cmd + Shift + Alt + E), apply Unsharp Mask at a small radius — around 0.3–0.8 px for web sizes — with a fairly high amount, and set the layer to Luminosity so it does not create colour fringes on edges.
Sensible dimensions
Full-width hero images rarely need more than 2000 px on the long edge; in-article images rarely more than 1200 px. Serve a 4000 px photo into a 800 px slot and you have wasted most of the bytes. Export at roughly twice the display size to cover high-DPI screens, and no more.
Strip what you do not need
Export As has a Metadata option — "None" removes camera data, and with it any GPS coordinates embedded at capture. Worth defaulting to for anything published, both for file size and because location data in a personal photo is not usually something you meant to publish.