Only load the minimum assets needed to render a page.
Easy to implement
8 High impact score
JS and CSS files should only be loaded if the page actually requires them, and no duplicate resources should be loaded, watch out for third-party libraries that quietly bundle in a copy of a library (e.g. jQuery, a chart library) you’ve already included elsewhere. PurgeCSS can help with dead code detection.
Two further habits worth building in: limit the number of third-party libraries and fonts you depend on in the first place, and evaluate loading non-critical dependencies (chat widgets, video players, map embeds) on a click or interaction event rather than on initial page load — the asset simply doesn’t cost anything for the visitor who never triggers it.