Mimic the swings of Dustin Johnson and Jon Rahm to completely stop fatting it

You might not be able to play like the best two players in the world right now, in Dustin Johnson and Jon Rahm, but I would highly encourage you to copy their swings if you typically 'FAT' the golf ball. 

With a lot of people I see who fat the ball, their arms go too much into extension through impact.... what I mean by this is that both the right and left arms are completely straight at impact. What I would suggest trying is, practice coming into impact with the right arm still flexed.

Check out these swings of Johnson and Rahm to see what I mean...

As they come into impact, the inside of the tricep and bicep is quite connected to the ribcage, and the right arm as a result is a lot shorter. 

When you start doing this, you might find you start thinning a few shots, but your body will react to the failure of thinning it and you will stay in your posture more. You will actually stay in more of an anterior tilt, where you are tilting forwards more through impact, and you will stay in great posture through impact. The right arm will maintain its flex coming into impact. 

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I also believe it can lead to a more stable clubface, whereas when the arms go into extension too much and the body is jumping out of its posture, you tend to find the torso stops rotating and the clubface can get a little more active.

It's something you can learn so well from Rahm and Johnson, who both keep that right arm a little shorter. You start to strike it a whole lot better.