It is interesting that in the Noble Eightfold Path which the Buddha presented as a way of experiencing freedom from suffering, mindfulness comes before samadhi. So it shows very clearly that what is important is learning to be mindful, learning to be aware, just knowing what is happening from moment to moment. From that the samadhi can come naturally. So in practical terms, when we are trying to learn to be aware of our breath, what we can try to do is to be aware of whatever is happening in our mind and body. Even if you realize that your mind is not concentrated, that your mind is not calm, just knowing it, just accepting it can make such a difference.