When I feel myself drifting off during lessons I like to focus using this idea of always checking form and movement, getting feedback from my body and knowing that I'm staying on the path.Like many people, once I have achieved basic competence in a skill, and can do it "without thinking", my mind tends to wander off as I go through the motions. I may even feel a little bored ...
But what martial arts has taught me is that this is usually the first plateau in learning. Looking back, I struggled to get to this point, and am relieved to have gotten even this far. Perhaps I am a little drained from the effort, and need time to consolidate.
Looking forward there are many more challenges to come. Littlefair's tip is one way to open up the training and to start exploring sensitivity, details and principles.
Nowadays, with a busy life, going through the same routines that I have followed for years is less frustrating and often somewhat comforting (like slipping on a comfortable old pair of gloves). But it is also exciting, because I no longer take my competence for granted, and know that with a bit of creativity I can exploit my familiarity as a starting point for a fresh climb into further learning and understanding.