Rule of thumb: a link text should describe the resource that it links to, so that when the text is read out of context the user will still know what to expect.
Link text should stand on its own. Some assistive software scans a page for links and presents them to the user as a simple list. In these situations, all the links will be read out of context. So it is important the text used in a link is descriptive and meaningful.
It also makes your text easier to scan visually, so that sighted users can more quickly find the information they’re looking for.