Anapanasati practice: what’s the correct way to focus on breath? I have practiced anapanasati for a while and encountered some difficulties. I can easily find my breath in front of nostril. Then I started to pay attention to the in-and-out of the breath continuously. But after a while, pain raised in my chest around heart. As I tried to focus more on the breath, the pain increased. In addition, if I suddenly stopped paying attention to the breath, I found my neck and shoulder very rigid and uncomfortable. I also felt exhausted after the meditation.

I’m wondering if I focus too much. Before I know anapanasati, I used to practice simple meditation like just relaxing and checking any thoughts if they arise. I felt much better by not paying attention to any object.

So my question is: what is a good “attention” to breath? Thanks!
There is no need to focus on the breath. 

The practise of the Buddha is to keep the mind without craving, without attachment, without past, without future. Silent still mind. 

When the mind is quiet, it will connect with the breath, itself, automatically. 

Experiencing the breath is merely the "sign" the mind is without craving. 


  And what is the faculty of concentration? There is the case where a monk, a disciple of the noble ones, making it his object to let go,
  attains concentration, attains singleness of mind.
  
  Indriya-vibhanga Sutta