(the 14th Dalai Lama)
Relaxing in such awareness is key. "Being present" is a requisite, but is not enough. Being present is full of anxiety, of desire to grab what's here and now "before it disappears," for as long as one doesn't fully accept impermanence, resists it, considers it a threat to what's enjoyable in the present.
This is very important when one is trying to appreciate the present while letting go of a painful past. Wanting to remember a sweet present is wanting to make the current joy more permanent; it is rejecting the present by projecting oneself in the future (as someone clinging to a particular view of the past!) and it is rejecting the impermanence itself (of memories). Letting go of the past is different from piling new memories up.
Without relaxing in the present moment, it is possible to be fully aware of tiny nuances and barely-noticeable quick transformations while not enjoying the activity at hand simply because one is tense in the awareness, trying to "get the best" out of it.
One needs to abandon the judgement of good or bad in conjunction with the awareness of impermanence. Using every precious moment is as much using what's pleasurable as using what's painful. Both holds lessons!