On-page SEO is everything you can directly control within a page: its title, its structure, its images. Unlike technical or authority SEO, it doesn't depend on server configuration or external links, so there's no excuse for not getting it right from day one.
Title and meta description
The title should include the main keyword naturally, be unique across the whole site, and be a length that doesn't get cut off in Google's results (around 60 characters). The meta description doesn't directly affect ranking, but it does affect whether someone clicks among several similar results.
Heading structure
A single H1 per page, summarising what it's about, and a hierarchy of H2s and H3s that organises the content into logical sections. Jumping from H1 to H3 without an H2 in between, or using headings purely for their visual size rather than their function, confuses both readers and Google.
URL and internal linking
A short, descriptive URL, without unnecessary parameters, helps more than it seems. Just as important is linking from other existing pages to the new one: an orphan page, with no internal link leading to it, takes much longer to get indexed and ranked.
Images and alt text
Every image needs a descriptive file name and alternative text (alt attribute) explaining what it shows, not just for accessibility, but because Google also indexes images separately, and that's a traffic source many websites waste.
Content and keyword density
The target keyword should appear naturally in the first paragraph, in some heading, and throughout the text, without forcing it artificially. Repeating it unnaturally to "optimise" the text usually has the opposite effect to the one intended.
Frequently asked questions
How long does it take to go through this checklist on a new page?
With practice, 15 to 30 minutes per page. Building it into the publishing process, rather than reviewing it afterward, saves having to go back over already-published content.
Is on-page SEO enough on its own to rank well?
No, it's the necessary base but not sufficient on its own. Without a healthy technical foundation and some domain authority, a perfectly on-page-optimised page can still fail to show up on the first page.
Does this review need repeating on pages published a while ago?
Yes, it's worth periodically reviewing the most important pages, since best practices change over time and what was well done a few years ago may have become outdated.