I practice by writing so...
Mindfulness might be the following...
My mindfulness scale is 1 to 10.
If I notice I am threatened by a large angry man 1 metre away from me who is shouting at me, then I am mindful10. Such that mindful10 is very easy to notice!
If I notice I am threatened by a small babies loud voice whilst in the shopping centre, I am mindful5. Such that I might be under real threat or not when I react startled to the noise.
If after being startled by a babies loud voice, I regulate myself back to calm and controlled, then I am mindful10.
If I notice I am not threatened by a quiet gentle person, then I am mindful5. Because a quiet gentle person has hurt me before, but many quiet gentle persons have been nice to me before.
If I notice I am not threatened by a normal tone of voice, then I am mindful8, because I consider normal tone of voice the optimal tone of voice for most situations.
Then after writing those down, reflecting along the way, I pause and reassess rationally and emotionally.