What are the various viral strategies for SEO?

What are the various viral strategies for SEO?

I have heard that viral strategies are the best bet to improve your website popularity today. I have seen many of my friends create viral videos and upload them online to instantaneous popularity. But are there any other viral strategies that I could use? What are the various strategies popular online? Would these, in any way, be considered as spam marketing? I have looked on your forum for SEO related answers and found much useful advice. I am hoping you would help me out this time as well. Please feel free to send in your thoughts and opinions.
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