Backlinks & Toxic links
Quality over quantity
Many think the more links, the better but it doesn't actually work that way. Too many low quality and/or spammy links and your website will lose Google credibility and therefore visibility.
You are responsible for the links that point to you
Since a few years already, you as website owner are responsible for the backlinks pointing to your site, so you need to constantly monitor, identify bad links and clean up your backlink profile. First step using the disavow tool then to try pro-actively to remove them.
Backlinks to avoid
Getting a backlink that appears on every page of a site is rarely a good idea especially if it not set as nofollow. First the position of the link on the page is a key factor so if your link is in the footer its positioning is all but optimal. Second, your numerous backlinks will in fact count as only one and its value will be minimal if negative. Other type of links to avoid: links from unrelated websites, from sites of different languages and/or countries and from websites flagged as spammy
Once you have identified those toxic links, the best is first to use Disavow Tool to inform Google you are aware of them and want to bring them to Google's attention. Please note that you need to be connected to the website's Search Console account in order to log into the tool. Google then advises you to actively get in touch with the respective webmasters and ask them to remove them.