Mindfulness can be practiced at 4 layers of our existence. i.e., the body, the breath, the thoughts, and the emotions. For a beginner, the mindfulness of the body, its positions, its movements and sensations, the breath, its state, and movement are of tremendous help to practice mindfulness and experience the state of balance and integration in life.
For example, while we are walking, we can become mindful of each step, the touching of feet on the pathway, the movements of legs, movements of arms, the surrounding sounds, the breeze touching the body, the sun rays touching our skin, the breath movement, etc. in a non-tense, relaxed and non-judgemental way. Similarly, when we are practicing mindfulness of our breath; we stay with the breath, we watch the incoming and the outgoing breath, the sensation of the breath, the movement of the breath and the rhythm of the breath in an effortless and non-tense way.
Once, one is firmly established in the mindfulness practice of body and breath, one can move further to the next 2 subtler levels of mindfulness practice. i.e., the mindfulness of thoughts and emotions. As we advance in the practice, we can expand mindfulness to our daily life activities.
Mindfulness is not something separate from us, it is not a concentration practice, it is all-inclusive. So, it is attending to ourselves at different levels and states in a non-reactive way.