When you have your model completed, make sure you have the right edge loops for where you place your bones. For the double rotation, you have to create another edge loop between the wrist and the elbow joint. Like that circled in this next photo.
The character I set this up in was called "Emo Boy." So, in his rig I attached his name to the bones which looked like this: (Note, red bones and controllers are for the right side of the rig, blue bones and controllers are for the left side, and yellow is for the spine, neck, and head. That is just my personal preference.)
Those are just the bones for the arm so that it's easier to follow along with this tutorial. If you didn't know, you should have the bones at the elbow joint at a slight angle so the IK chain can deform properly. Here is a picture of the arm bones placed in the Emo Boy model.
After the bones have been placed in the correct spot, you then create four dummy helper objects. You name them according to
the names of the bones, for example;
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