Since I use these ear wires to use up 28-gauge wire off cuts, I tend to prepare the coils first, winding lengths of wire and then chopping the coils into the desired length.
As a rule, you will use 1" of 28-gauge wire per 7 coils, when wrapping around 20-gauge wire.
Take a piece of 28-gauge wire (the off cut I am using here is 6" long). You can either use an off cut of 20-gauge wire as a mandrel, or cut a new piece 2" long (which can be used for the actual ear wire later). Coil the 28-gauge wire around the 20-gauge wire, leaving a 1" tail (use this to hold the wire in place whilst coiling). Keep the 28-gauge wire at a 90° angle to the 20-gauge wire at all times to ensure your coiling is straight and neat.
Every 5 or 6 coils slide your thumb nail along the 20 gauge wire pushing the coils tightly against each other (whilst holding the 1" tail against the thick wire with the other hand).
Continue coiling until you have used all the 28-gauge wire.
Note:- You will have approx ½" of 28-gauge wire either end which you will not be able to use as it becomes kinked where you have been holding it.