Gil Fronsdal leads a guided meditation on the breath as a fundamental practice for mindfulness and to familiarize the self to breathing, then to the body.
He starts with instructions to a proper seating posture. Starting with deep breaths, being aware of the body as you inhale and then letting go and relaxing upon exhaling.
The process of mindfulness is not about judging what you're aware of, but by being familiar with your experience, with your breathing.
Then familiarizing yourself about your body, without judgement but just loving recognition of how your body is. Tired, relaxed, tightness. Being mindful of how things are is central to the practice. Part of being mindful is how we're aware. To hold every experience in our hearts.