A: with one hand at the shoulder, midway between the sleeve and the neck.
B: with the other, halfway down the shirt, parallel with your other hand.
Lift the shirt so that it hangs in front of you. Uncross your arms, without letting go of the shirt, and pull fold taut as you do so.
Place the hanging sleeve on the work surface, and neatly drape the folded portion over it to finish.