On page SEO is everything you can change on the page itself to help it rank and to help a reader who lands on it. Unlike links from other sites, all of it is within your control, so it is usually the fastest place to make progress.
This article works through the changes in order of how much they matter. It assumes you already know which phrase the page is meant to target.
Answer the question in the first paragraph
Most pages bury the answer. Somebody arrives with a question, reads three paragraphs of introduction, and leaves. That behaviour is visible, and it works against you.
So say the thing first. If the page is about how much a service costs, the opening paragraph should acknowledge that. You can add nuance underneath. What you cannot do is make a reader hunt.
Practically, the target phrase belongs in that opening paragraph too. Not because a search engine counts it, but because using the words a reader searched for confirms they are in the right place. What a search engine does count is set out in how a page earns a ranking.
Write a title that earns the click
The title is the single most important element in on page SEO, and it does two separate jobs. It tells a search engine what the page is about, and it persuades a person to choose you over nine other results.
Keep it near sixty characters, because longer titles get cut off. Put the main phrase near the front. Then, if there is room, add the reason somebody would pick this result: a year, a promise of brevity, a specific angle.
Avoid stuffing. A title reading "Plumber London Plumber Near Me Best Plumber" is worse than a plain one, because nobody clicks it.
Use the meta description as advertising copy
The description underneath the title does not affect rankings directly. However, it heavily affects whether anybody clicks, and clicks matter. Treat it as a small advertisement rather than a summary.
Aim for roughly 120 to 155 characters. Include the phrase, since a search engine bolds matching words and that draws the eye. Above all, say what the reader gets.
Structure the page with real headings
Headings are not decoration. They are how a reader scans, and how a search engine works out the shape of your argument.
The page title is the top level heading, so everything inside the article starts one level down. Use a heading whenever the subject genuinely changes. As a rule of thumb, if a stretch of text runs past about three hundred words with no heading, a reader scrolling on a phone has nothing to grab.
Write headings as the questions people ask, not as labels. "How long does it take" beats "Timescales" every time, because the first one matches how somebody searches.
On page SEO for images
Every image needs alternative text describing what it shows. This is first an accessibility requirement, because somebody using a screen reader depends on it. It is also the only way a search engine knows what the picture contains.
Describe the image plainly. "Engineer replacing a boiler valve" is useful. "boiler boiler repair boiler service" is stuffing, and it fails the reader who needed the description.
Compress your images too. A slow page loses readers before they see any of your careful writing, so the fastest on page SEO win on many sites has nothing to do with words at all.
On page SEO for internal links
Internal links are the most underused part of on page SEO. When one page links to another, it helps a reader continue and tells a search engine which pages you consider important.
Link with descriptive words rather than "click here". The words in a link tell both the reader and the search engine what to expect on the other side. Meanwhile, a page with no links out of it is a dead end, and dead ends are where visits finish.
Keep the address short and stable
A web address should describe the page in a few words, use hyphens between them, and then never change. Once a page has been live and has earned rankings, changing its address means asking a search engine to relearn something it already knew.
If you must change one, redirect the old address to the new one permanently. Otherwise every link anybody ever made to that page breaks quietly.
Where to start with on page SEO
Take your five most important pages. Rewrite their titles so the main phrase sits near the front and the title reads like something a person would choose. Rewrite their descriptions as advertising rather than summary. Then check the opening paragraph of each and make sure it answers the question instead of introducing it.
That is an hour of work with more effect than a month of tinkering elsewhere.
Frequently asked questions
What is on page SEO?
It is every change you can make on a page itself to help it rank and to serve the reader better. That includes the title, the meta description, the headings, the opening paragraph, the images and their descriptions, the internal links, and the address. All of it is within your control, unlike links from other websites.
What is the difference between on page SEO and technical SEO?
On page work is about the content a reader sees and how it is presented. Technical work is about whether a search engine can reach, load and understand the page at all. They overlap around speed and structure, and most projects need both, but the questions they answer are different.
How long should a title be?
Around sixty characters is a safe target, because longer titles get cut off in search results. What matters more is that the main phrase sits near the front and the rest gives somebody a reason to choose your result over the others on the page.
Where does the meta description fit into this?
Not into rankings directly. It decides whether anybody clicks, which matters a great deal. Write it as a short advertisement rather than a summary, include the phrase so matching words are highlighted, and say plainly what the reader will get from the page.
How many times should the keyword appear on the page?
Often enough to read naturally and no more. If a phrase appears so often that the writing sounds strange when read aloud, it is too often. Using related words and the questions people actually ask does more good than repeating one phrase.
Do headings really matter for on page SEO?
Yes, for two reasons. Readers scan headings rather than reading in full, especially on a phone, so headings decide whether somebody stays. They also tell a search engine how the page is organised. Writing them as the questions people ask makes them work harder.
What alternative text should I write for an image?
Describe what the image actually shows, plainly, as if to somebody who cannot see it. That serves people using screen readers and it tells a search engine what the picture contains. Repeating your keyword instead of describing the image fails both.
Should I change old page addresses to include my keyword?
Usually not. A page that already ranks has earned that address, and changing it asks a search engine to relearn what it knew. If you genuinely must change one, redirect the old address permanently so existing links keep working.