I would say that any list of the "top 5" would be subjective, so I will provide the one factual, objective and unavoidable common denominator between most (if not all) off page techniques - top notch content. The techniques themselves will inevitably create differences in the type of content you need, where it is published, the sales funnel you create and so forth, but the level of engagement you can generate with your content is what will ultimately determine your results.
1. Daily content Publishing on your Blog
2. Guest Posting
3. Outreach for Mentions and Links
4. HARO Picthes free backlinks from High authority websites
5. Discussion in forums and Communities like reddit, quora, etc..
I think USG or user-generated content, SEO optimized title, and content that actually answers questions.
For example, if I do a quick search with the question "what is dropshipping?" these are the 3 sites that rank according to Google results (or at least, in my area, I'm from the US): site 1, site 2, and site 3.
They all have something in common. When you go through SEO tools like Ahrefs or SEMrush, you'll see that all three made a significant effort in building a guestposting profile. Their titles are all directly related to the question, and the content are top-of-the-notch. The best thing I noticed though was when I was searching through content and going through forums when I was learning about dropshipping, I encountered these three same articles mentioned by the people! This is where "word-of-mouth" comes into play. These three websites are known to have a reputation with dropshipping content, hence they are mentioned organically, which, to Google, is a huge plus! Since people are talking about you, we'll push/crawl your content further for more people to see!