A slow WordPress site almost never has one cause - it is the sum of five neglected things, each of which looks innocent on its own. The good news: the repair order is always similar, and most of the gain comes from the first few steps. This guide walks through them from biggest win to cosmetics, for a regular company site; stores have their own quirks, which I covered separately in the piece on a slow WooCommerce store.
Step 0 - measure before you start
Without a measurement you do not know whether things improved. PageSpeed Insights (free, from Google) gives you a score for mobile and desktop plus a list of problems. Write down the starting score - that is your baseline. How to read those numbers without falling into the usual traps is covered in the speed mini-audit; the short version: look at the mobile data, it is harsher and more honest.
Step 1 - hosting (the foundation nobody wants to hear about)
A site on the cheapest possible hosting, shared with hundreds of other sites, will not be fast no matter what you do next. How to tell the problem is here: a clearly stretched time to first byte (TTFB in your measurements), a site that is also slow inside the admin panel, and slowdowns at peak hours. Decent hosting with a current PHP version (8.1+) costs on the order of 200-800 PLN a year in Poland - the cheapest possible investment in speed. When changing servers helps and when it does not is a decision of its own, but without a healthy foundation the remaining steps are furniture arranging in a flooded flat.
Step 2 - caching (the biggest single win)
WordPress builds every page from scratch on every visit: queries the database, assembles PHP, renders. A cache saves the finished result and serves it to the next visitor without any of that work - often the difference between 3 seconds and half a second. A caching plugin (commercial or a good free one) plus sensible configuration settles it for a typical company site. Watch out for doubling up: two caching plugins at once, or a plugin cache stacked on a server cache, can produce the opposite effect.
Step 3 - images (the most common single sin)
A photo straight off a phone dropped into a post weighs 5-10 MB; on the page it needs 100-300 KB. Multiply by ten images on a page and you have your answer for why the site drags. The prescription: modern formats (WebP/AVIF), dimensions matched to where the image is displayed, and lazy loading so images below the fold load only on scroll. Optimization plugins will process an existing media library in bulk.
Step 4 - plugins and theme (slimming down)
Every active plugin is potentially extra CSS/JS loaded on every page - including pages where it is not used. Go through the list: what genuinely does something? What is hanging around “in case it is useful one day”? A typical site after a few years carries dozens of plugins, half of them redundant. Same with the theme: multipurpose builders load their framework on every page. Swapping the theme is a more serious operation - but it is sometimes cheaper than patching forever.
Step 5 - the database and the small stuff
Post revisions counted in the thousands, transients left by long-deleted plugins, a trash bin full of spam - after a few years the database needs a vacuum (via a plugin, with a backup first - see the safe updates checklist). Plus: a current PHP version, disabling unused scripts (emoji, embeds), and fonts served locally instead of from external servers.
What helps: make ONE change at a time and measure after each. Installing five optimization plugins in a single evening is a lottery: you do not know what helped, what hurt and what conflicted. Optimization is a process of elimination, not an incantation with plugins.
FAQ
Where do I start if I have time for one thing? Measurement plus caching. Half an hour of work, usually the biggest single jump. Images next.
Will a plugin that “speeds up everything” solve it? Good optimization plugins do a lot (caching, images, script slimming), but they will not fix slow hosting or dozens of redundant plugins. A tool is not a diagnosis.
How much does professional speed work cost? I give a concrete number after a diagnosis - first I check what is actually holding the site back, because everything depends on the state I find it in. I always start with a measurement and tell you what will give the biggest gain, before you pay anything. How I approach that pricing for stores I described in the piece on what it costs to speed up a WooCommerce store.
Sitting on this yourself and unsure where to start? I speed up and repair existing sites and stores - Core Web Vitals, outages, the features that are missing. Tell me what is happening and you will get a concrete quote with a date.