what is the main SEO factor of today era?

There are a number of factors that affect how a website is ranked and search engines such as Google are constantly altering their ranking process to ensure that we all get the most relevant search results. Ensuring that your website ranks highly in searches conducted by your target audience is the essence of Search Engine Optimisation.
http://www.webforcefive.com.au/search-marketing/search-engines-why-seo-is-important

 

for me its content... and the way we present the same.

https://www.inovies.com/insights-vi...formula-for-user-engagement-to-a-website.html

 

What is the desired keyword density? in %

 

Do a site analysis
competitor analysis
keywords analysis
choose a long tail keywords
optimize on-page elements
Quality content update
start a blog
share in social media
do a niche oriented link building

 

1. Good onpage optimization (quality & unique content, page structure, meta tags)
2. Good offpage optimization (building quality backlinks)
3. Social interaction of website on popular social platforms

 

On-page optimization is the main factor now a days.

 

its time for AMP'S

 

Links, content and honestly having a PBN is required to ranking in competitively niches. If you aren't using a PBN, then someone else will if there's money to be made there.

 

Today era the main motive is quality instead of quantity. Focus on given below some suggested task

Strong initial analysis
Proper and good keyword research
Complete on-page for website
Post quality and user friendly content
Also mobile friendly and page speed is mandatory.

 

I think you need to focus on 3 issues: Proper keyword research, unique quality content,backlick from relevant high-trust sites.

 

I think there is a big weight on content. Content is very essential to have to more followers to your campaign.

 

Well it is not just a factor but always and will be a golden rule, "Quality over quantity", add some relevancy too.