A favicon is one of the smallest images on a website, but it appears everywhere: browser tabs, bookmarks, search results, pinned shortcuts and mobile home screens. The mistake is trying to shrink a detailed logo into a 16-pixel square. At that size, complex text and fine lines disappear.
The best favicons are simple. A single letter, mark, shape or high-contrast symbol usually works better than a full wordmark. Before converting formats, simplify the source artwork and crop it into a square.
Prepare a square source
Start with a 512 x 512 or larger square PNG if possible. Use transparency if the icon shape is not a full square. If your source is a JPG, remember that JPG has no transparency, so it will always have a rectangular background unless you edit it first.
Check the icon at small sizes before publishing. Zooming into a large preview is misleading. A favicon has to remain recognizable when it is tiny, surrounded by browser UI and possibly shown on both light and dark themes.
Export the right assets
Modern websites often use SVG or PNG icons, but ICO is still useful for broad favicon compatibility. Convert the prepared square image into ICO only after you are happy with the crop, contrast and background.
Keep a larger PNG or SVG master for future updates. If you later need app icons, social avatars or manifest icons, generating them from the master will look cleaner than scaling up a tiny favicon.