There are some common indicators of a backlink being high quality. Please note that no one can tell you for sure how search engines measure the quality of backlinks. The further information is our experience-based recommendation.
The most valuable backlinks are those editorially placed somewhere within the content (i.e. not in the footer or sidebar). Basically, if website owners refer to your page voluntarily, they give you a valuable vote of confidence.
Authority of the linking page/site. You can determine how much of “link juice” you’re getting from a given backlink by the authority of a particular page that links to you — its URL Rating (UR). (You can find more information about Ahrefs UR metric here.) As a general rule, a link from a high authority site will be more powerful than a link from a low authority one. We at Ahrefs use the Domain Rating (DR) metric to measure an overall website authority.
Besides DR and UR metrics, what also matters is a number of outgoing links a website has. A backlink from a website (domain) or from a web page that links to hundreds of other URLs will be less valuable than the one from a website with just a few outgoing links.
“Do-follow” links are preferable. At the same time, SEO community hasn't come to an agreement if no-follow links help you rank or not. Basically, if you have a chance to get a no-follow link from a high-quality website, then go for it.
Our research has shown that an anchor text might have an influence on the quality and relevancy of a backlink. (You can find the full research here.) It’s essential for search engines to be able to choose the right keywords to rank your content for, that’s why the anchor text, as well as the text that surrounds it, should be topic-relevant.