How to know what everyone is searching?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  vo thang: hi Edwin,
  I have the question : How to know what is everyone searching ? Where do I find this big data ?
  
  Why do I have this question ? Because I will sell things which they need or design the website for this demand.
  
  Thank you very much
• 
  ?ukasz Rogala: Google Keyword Planner, Google Trends, straight from Google, 3rd party tools like Searchmetrics, Semrush.
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  Edwin Jonk: Cross-linking because this post is quite similar to ;
  https://plus.google.com/112793401664176821452/posts/cn9kYfBLCcy
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  London SEO Consultants: Another idea is to use google alerts and search operators such as "keywords" ; etc - which will pull data for anyone mentioning the keywords together - or by using site:domain "keywords" to find anyone mentioning the terms on a site
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  Edwin Jonk: Another, quite simple, one is to look at auto-complete. An example I learned from +Tony McCreath ;is [guitar strings]. If you fill that in, you get auto-complete. For me, it suggested [guitar strings wallmart]. So it can make sense for a guitar string seller to write a blog post about the fact that you are cheaper/better than Wallmart.
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  ?ukasz Rogala: Instead of that use Ubersuggest.org:)
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  London SEO Consultants: keywordtool.io is another one, similar to ubersuggest.org - both are good
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  Ankit Goyal: Keyword planner or Bing Keyword Tool is the best to find the search volume.