When I was suffering from clinical depression and anxiety, I never really understood the suggestions I read to simply state to yourself, 'I am feeling anxious', or 'I am feeling sad'. Stating the obvious didn't seem to me to be a step to mental health. Now I understand this is a step to mindfulness, to increased self awareness.
Detaching from this observation is where the real benefit comes, and this is what Tolle talks about. Making the observation without an emotional payload is the key. This translates to me into saying, 'Wouldja look at that! There's some anxiety right there. Huh!' instead of a silent wail of despair that spirals down into the dark.
As for becoming good at mindfulness or mediatation, I believe that's irrelevant. It is the doing of it that is good, bringing focus back to breath after observing the interfering thought and offering it acceptance. It is through the acceptance part that the light begins to enter.