As I have explained already several times, in my coaching work I like to split reactions on wing shots depending on that if the wing shot comes from small, normal or from big angle of shooting.

Here are a few examples and explanation of how a goalkeeper should react on wing shots from SMALL ANGLE OF SHOOTING.

Important reminder – if the wing shot comes from a small angle– the goalkeeper has to just position properly, observe, wait for the shot and then react accordingly! 
There is NO NEED to make a step forward when the shot comes from small angle, because in that way goalkeeper would just unnecessarily open the front post of the goal!

Check out this video for more clarification: