To play shinobue, you blow air into it... right?? Not exactly...
In Japanese, the verb for playing shinobue (or any wind instrument) is "fuku." The word "fuku" is to blow. When I first met my teacher, Bunta Satoh sensei, he said to me, "Fui cha dame." meaning "No blowing."
How can anyone play the shinobue without blowing air???
Then he elaborated more, saying, "Don't blow the air (with your mouth/lips). Push the air from your stomach. Your lips stay relaxed and soft like you are kissing a baby."
When a note doesn't come out right, the first thing our instinct tells us to do is to blow harder, often tightening our lips even without noticing. We shouldn't. Instead, we should keep our lips relaxed and use our stomach muscles to push the air up from deep below.
This is hard to do at first. It took me more than two years, especially because I played the shinobue with the tight lips and blowing hard method for an entire year prior to meeting Bunta sensei.
So don't get into a bad habit. Know that your lips need to be relaxed, and your breath needs to be coming from your stomach.
Most likely, you can't do it that way right away, but if you keep that in mind when, even by accident, you do it right, you will realize that's what I am talking about!
And you will know it because your shinobue will thank you by sounding a beautiful tone you didn't know it could create before.