In the list that shows all artists, tap the cover art that is directly left of the artist name. (See image) and then make sure the shuffle toggle is turned on in the full screen player.
*edit*
And in iOS 9 they added an actual shuffle button above all the artists albums you have once you're tapped into an artist "page". However doing it the method I first mentioned (shown in the image) is quicker, since you don't need to tap into the artist at all.