How do I know which change I made was the right one?

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

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  Michael Martinez: There is no way to directly attribute a cause to anything in search engine referral traffic. The best you can do is say, "Well, I did X and Y happened. Let me try that again and see what happens."
  
  Repeated success doesn`t mean you`ve solved the riddle of the search engine. But it gives you opportunities to build even more success.
  
  In SEO we often succeed in spite of our assumptions about what is working.
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  Bill Hartzer: Michael is right, I also recall that they have a part of the algorithm that is used solely to make sure that the timing is confusing to SEOs.
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  Becky Westmoreland: I’d also add that if overall it ranking changes sometimes it means you lost or gained keywords so averages can also bounce that around
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  The-Nomad Sam: GSC shows data at least 24 hours behind so I doubt you would ever see same day changes, if you’re querying your morning actions.
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  David Gizzarelli: The-Nomad Sam I`ve seen it report different delay times
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  David Gizzarelli: I also want to note that it`s interesting how I cannot have an increase in one variable without another variable going down. If my position is down, I`m getting more impressions, the opposite is true. Which of the four variables is the best indication that your site is performing well or better?
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  Michael Martinez: You want more clicks, basically.
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  Tom Riley: David Gizzarelli you avg position can go down but your overall impression goes up this is quite common.
  
  If you are gaining rankings for new keywords these keywords may rank 100+ therefore bringing the `average` down but impressions up.
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  Tim Capper: Impossible to really tell - unless you make 1 change wait a month, make another ... wait (oh and tag your changes in Analytics)
  
  Which would never be practical :)
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  Flavius Fotea: SEO does not work like this. Perhaps your whole SEO changes made your site rank well. Perhaps some of your old stuff that you thought were good, were not at that time and now Google may have had a small update (they always have) which make that stuff that you placed about 1 year ago to be relevant. Maybe some internal links that you didn`t even put too much thought into.
  
  Google will never tell you "hey, I found THAT stuff that is right so I`ll increase your rankings". Nope, you just have to do what you think it`s right and hope for the best. That`s mostly how SEO works. Or look at what experts do, but think about it for a second: If you knew a great secret about how to rank your websites, would you tell other people? :)