The best backlinking method is organic backlinking. Organic backlinking refers to a backlinking practice where people voluntarily give you backlink. If your web contents are useful, interesting, and well written, people will voluntarily give you backlink. Forum signature and forum profile link are the easiest and the most effective backlinking method as you will get quality do follow backlinks. However, not all forums give you quality backlinks or dofollow backlinks. You can also do guest posting for backlinking. Guestposting means you publish articles on other blogs and websites and share link to your website through anchor text. You can get quality backlinks through guest posting.
It is risky, however private blog network is also one of the ways to get free backlink. In order to create backlinks through private blog networks, you have to publish a lot of blogs and share your website link on these blogs.