Kubo is told in his dream to "follow the setting sun" in order to find the helmet. He immediately wakes up and leads his group into the rising sun. Then the shadows indicate light is behind them, then in front again.
The goof item below may give away important plot points.
Incorrectly regarded as goofs
The title might suggest that Kubo has a shamisen with two strings, Kubo's shamisen has actually 3 strings, The two strings in the title are not the the strings on the shamisen, they are the parents. Or, life and death - there is some deliberate ambiguity as to what the two strings are.