They screwed with the user interface and made it hard to find:
1. Open the "now playing" tab (where you can see the art, the forward/back/pause buttons, volume control).
2. Swipe to scroll up- VERY NON-INTUITIVE
3. There you will see the "shuffle" button highlighted, tap to turn it off.
Personally, the artwork should be shrunk to keep such an important button visible. And the "shuffle" button at the top is useless, you can just hit "next" if shuffle is on. I don't understand why Apple keeps changing good UX decisions to extremely poor UX decisions. Jobs would roll over in his grave.