How can I expand my knowledge about off-page SEO?

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I am well-versed in the general criteria of off-page SEO, but my knowledge of how to improve it is quite limited, to say the least. I have dedicated a lot of effort to on-page SEO, but without the support of off-page SEO, the results are always lacking. Can you share techniques, information, etc.? How should we approach techniques for acquiring backlinks, and how can we obtain them from the same industry, for example?