I once bought a fat quarter folded like this from a LQS. It stored so easily and looked so neat. I hope you can understand how this is done by these pictures. I will attempt to show and explain it to you.
this is what the finished fat quarter should look like
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fold the fat quarter twice, lengthwise
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then fold in half again
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then tuck in the folded side into the selvedged side
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bring selveged edge up halfway
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