Link building is important for ranking your content, however, these days I don't bother trying to build backlinks manually by submitting my links on various websites through strategies like guest posting, signature link, blog commenting, directory submission, article submission, etc. That’s because these link building methods aren't liked by Google and other search engines. For instance, guest posting is frowned upon because it's seen as trying to cheat the system b y creating backlinks through some kind of arrangement. Link exchange is also not favored by search engines. These days, I mostly strive for organic backlinks. I publish high quality content so that people share my link because they genuinely like my content. If you do decide to build links manually, only use sites that are ranked higher than yours.