This meditation is from Thich Nhat Hanh's book, Under the Rose Apple Tree,
"When I breathe in, I know that I am breathing in." The "I know" is very important. Your breath is the link between your body and your mind. It's so nice when you are in touch with that link; then you are in touch with everything in yourself, body and mind. And right away, you are master of yourself in any situation. You are not carried away by anybody or anything, including your thoughts.
Your mind is fully with your body and your whole being.
When you start to know that you are breathing in or that you are breathing out, you start to know what you are doing - whether you are sitting, standing, or walking. So knowing is very important.
Don't think that practicing Buddhism is very difficult. It's not difficult; it's easy.
Can you breathe in and out and know that you are breathing in and out? Breathing in and breathing out - that's mindfulness. Practice being mindful with your breath first, and then you will be mindful with your body and with your mind; you will be mindful about everything that happens around you.
Breathing consciously, mindfully, is a very good practice. In our daily life, if we don't know how to breath mindfully, how to stop thinking, we cannot get in touch with the wonderful things in life like the sunshine, rivers, clouds, our family, and our friends. So breathing is very good.
Below is a gatha, a poem, that you can say to yourself as you sit for a few minutes and breathe: