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Lots of methods to how you reach out to them, but sounds like prospecting and finding them in the first place is the bigger issue.

For prospecting, go start by looking for lists of blogs, eg "top gardening bloggers". Also look for non-bloggers, eg "top gardening instagram accounts". Google obvious content, eg if you're looking for fitness blogs, search "best upper body workouts" or "post workout protein options" and you'll find sites that might not show up for "top fitness bloggers".

Gather them all up in a spreadsheet. Find contact info. Interact on social. Email and introduce yourself. See if you can offer a guest post with some actual highly relevant titles that they'd be interested in. It helps to already have some decent content you have produced to lend you more credibility with them, eg "here's a few past things I've published on similar topics."

Consider expanding the process with tools like LinkProspector, Buzzstream, Pitchbox, Just Reach Out (this one seems to have good training wheels for people new to outreach) - that can help you scale up the number of sites you can find and contact. But it helps to use them once you have done the process a couple times.

As you mentioned, will take awhile when you don't know the niche. But you can learn the space pretty quickly

We have found that visitors who arrive at our site through search are over 10x more valuable than visitors who arrive from social media.   So, if we have content, we post it on our site, optimize it to pull traffic from search, and promote it to all of our visitors by posting links to it in many relevant locations.

Getting a shout out through social media might produce a one-time spike in traffic when the content is new, but an article on the website will pull traffic from search for years and years.  That  traffic from search will be more valuable.

By keeping all of your content resources on your own site, will enable your content library to grow faster and larger.  And, if you have done a good job on that content your visitors will see it and share it on social media for you.  Again, this is not a one-time blast, but a slower but steadier stream of sharing that will last for years and years.

Also, when you share your content through influencers, they will become your competitors in search, they can use it to drive affiliate salesl  And, there will be a lot of opportunists watching the influencer, and some of them will grab your content, mash it up, rewrite it, and you will have instant competitors for your valuable ideas in search and linking to Amazon.

The approach described above has the best opportunity of working if you can produce highese quality content.  If you can't do that, then it doesn't matter what approach you decide to use.

I would create best-on-the-web content and place it on my own site.

Brace yourself for another clunky guide from mr.

I prefer to start with outreach and write content after we've reached an agreement.

Here's what I do:

1. Get a list of relevant keywords
2. Repeat the "creating links to search queries in Notepad ++" from my previous answer to one of your questions
3. Only this time instead of simply creating queries like google.com.ua/search?q=best+cars you need to add an inurl:blog operator, so your links will look like **google.com.ua/search?q=best+cars+inurl%3Ablog **this link will provide you with list of blogs that have content about "best cars"
4. Generate such links for all of your keywords (again, see previous question and answer)
5. Crawl the SERPs with Netpeak Spider or Screaming Frog to fetch domain addresses
6. Once you have your domains you need to get thei emails, you can use tools like hunter.io or any other email harvester or search for those manually
7. you can also crawl these websites with spider or frog and search for the following regular expression: **[a-zA-Z0-9][a-zA-Z0-9.+-]+@[\w-.]+.\w+ ** this search will find any text on a website that looks like **something@something.tld **
8. Netpeak checker (not spider) has a preset setting to fetch email addresses: https://i.imgur.com/BzhzjHD.png but it crawl only URLs you upload, not entire website, so you'll have to get the list of at least 100 pages for every website on your list and then fetch email from those URLs. You can set spider or frog to get you list of top-100 ursl for websites you found.
9. You need to create personalized and automated emails that you will send to these websites. I recommend using **Reply.io **this is my favorite email marketing tool, period. It allows you to send out a chain of personalized emails (Hi [name] I was reading [website] blog. And thought you might want to check out [Thing]) to all of your prospects, and gives you all sorts of valuable analytics data so you can improve your campaigns. I usually create chains of 3 emails and prospecst receive one of these every 2-3 days. So if they ignored my 1st email they'll receive second one in 3 days, if they ignore that one they'll get another email in 2 days and if they ignore the last email that's it. But oper-rates and reply reats on campaigns I've ran were outstanding. With 3-letter chains on 200 prospects per campaign we're getting 70% open rate and up to 30% reply rate.
10. Once you get in touch with bloggers it's up to you to close the deal.

Don't hesitate to contact support of netpeak software, frog, hunter io, reply io and others for help. it always works.