Website Speed Optimisation: Practical Fixes That Make a Difference

Visitors rarely complain that a website is slow. They simply leave. A sluggish site makes paid ads less efficient, weakens the experience for organic visitors and makes the whole business look less polished than it is.

The good news is that most speed problems come from a small number of causes. This guide explains how to measure speed properly and which fixes tend to make the biggest difference.

Start by measuring the right things

Google’s Core Web Vitals are a sensible framework because they measure what visitors actually experience. The thresholds for a “good” result are:

• Largest Contentful Paint (LCP): 2.5 seconds or less. This is how quickly the main content appears.
• Interaction to Next Paint (INP): 200 milliseconds or less. This is how quickly the page responds when someone taps or clicks.
• Cumulative Layout Shift (CLS): 0.1 or less. This is how much the layout jumps around while loading.

Use two kinds of data. Field data, shown in the Core Web Vitals report in Google Search Console and in PageSpeed Insights where available, reflects real visitors. Lab data, from tools such as Lighthouse, is a controlled test that helps you diagnose causes. Field data tells you whether there is a problem; lab data helps you find it.

Test your most important templates, not just the home page. A service page, a blog post and a product page often behave very differently.

Fix images first

Images are frequently the largest files on a page and the most common cause of a slow LCP. Practical fixes include:

• Resize before uploading. A photo straight from a camera or phone is usually far larger than any screen needs.
• Use modern formats. WebP and AVIF usually produce much smaller files than JPEG or PNG at similar quality.
• Serve responsive sizes. Let the browser pick a smaller image for smaller screens using srcset.
• Lazy load images below the fold, but never the main hero image, which should load as early as possible.
• Set width and height attributes so the browser reserves space and the layout does not shift.

Reduce and tame JavaScript

JavaScript is the usual culprit behind poor INP. Every script has to be downloaded, parsed and run, and heavy scripts keep the browser busy when a visitor tries to interact.

• Audit third-party scripts. Chat widgets, tracking pixels, heatmaps, social embeds and A/B testing tools all add weight. Remove any your team no longer uses.
• Defer what is not essential. Scripts that are not needed for the first view can load after the main content using defer or async.
• Load tools only where needed. A booking widget used on one page should not load on every page.
• Review plugins. On WordPress in particular, plugins often add scripts and styles to every page even when they are only used on one.

Handle fonts and CSS carefully

Web fonts and stylesheets can delay the first render and cause text to jump when the font arrives.

• Limit the number of font families and weights. Each weight is a separate file.
• Host fonts on your own domain where practical and preload the one or two used above the fold.
• Use font-display: swap so text appears immediately in a fallback font.
• Remove unused CSS, which often builds up in themes and page builders over the years.

Get the server and caching right

No amount of front-end work can fully make up for a slow server. If the time to first byte is consistently slow, look at the foundations:

• Hosting quality. Very cheap shared hosting can struggle under modest load. Choose hosting that suits your traffic and platform.
• Page caching. Serving pre-built pages rather than generating each one from scratch is one of the most effective fixes for CMS-driven sites.
• A content delivery network. A CDN serves files from locations closer to your visitors, which helps if you have an international audience.
• Compression and modern protocols. Make sure text files are compressed and the server supports HTTP/2 or HTTP/3.
• Up-to-date software. Newer supported versions of PHP and your CMS are often faster as well as more secure.

Stop layout shifts

CLS problems are usually caused by content that arrives late and pushes everything down. Common sources are images without dimensions, adverts or embeds without reserved space, cookie banners that insert themselves at the top of the page and late-loading fonts. Reserve space for anything that loads after the initial render, and show banners as overlays rather than pushing content.

Prioritise by impact

It is easy to chase a perfect score in a testing tool. A better approach is to focus on the pages that matter commercially and fix the biggest issues first. A reasonable order is:

1. Your highest-traffic and highest-converting templates.
2. The largest single problem on each, often the hero image or a heavy third-party script.
3. Site-wide improvements such as caching, hosting and font loading.
4. Smaller refinements once the fundamentals are in place.

Keep it fast over time

Speed tends to erode as new plugins, scripts and images are added. Check the Core Web Vitals report in Search Console monthly, test key pages after any significant change and agree simple rules for your team, such as a maximum image size and a sign-off step before adding new tracking tools.

Key takeaways

• Measure with both field and lab data, focusing on LCP, INP and CLS.
• Images, JavaScript, fonts and hosting cause most speed problems.
• Remove third-party scripts you do not need and defer the rest where possible.
• Prioritise the pages that matter most to the business.
• Make speed part of ongoing maintenance, not a one-off project.

If your site feels slow or is failing Core Web Vitals, SEO Fleet’s website speed optimisation service can diagnose the causes, fix what matters most and help you keep the site fast as it grows.