Links, you know them. The clickable pieces of text that take you to another page on the website (internal links) or to a completely different website (external links). A healthy link structure and the authority you build with it are part of link building. During an SEO audit, it is only a small effort to also verify the following things:

• Broken links: these are links that no longer work, for example, because the page no longer exists. Remove or adjust to a proper destination!
• Pages with too many outgoing links: if there are too many external links on a page, alarm bells start ringing at Google. This is because it may indicate link exchange where you exchange links to your own website for a link to another website. In principle, this is against the rules of the search engine. So be careful with the amount of external links.
• Dofollow links: if a link has a dofollow tag, the link passes value to the destination page. Don't want to pass on value? Then add a nofollow tag.

On-page SEO parameters are snippets of code on a web page. They are not visible to the visitors of that page, but they are visible to search engines. The most important parameters are the metatitle and the metadescription. 

• Header tag: also called H1. It is the title of the text on a web page. There should be only one H1 on the entire page. Subtitles, denoted by H2 through H6, are allowed to appear multiple times. When auditing, also check that the H1 is not too long. Preferably no longer than 60 characters.
• Meta title: this is the title that appears in the SERPs and leads to the page in question. Also make sure that it is not too long and that it includes a relevant keyword. 
• Meta description: this is the text snippet below the meta title in the search results. A common mistake is that the text snippet is too long and therefore gets hyphenated by Google. So make sure the description is the right length (150 characters) and choose a unique text, not one you use for every page. 

In the H1, meta title and description, it is recommended to use relevant keywords. You normally already have these at hand thanks to a thorough keyword research.