Contrary to what many non-musicians think, practicing means being mindful, not mindless. One way to stay mindful is to ask ourselves from time to time what—specifically—we’re trying to accomplish at that moment.
This question has many good answers: Trying different fingerings, and noting their effects on articulation and phrasing. Dancing the rhythm—getting up and dancing—and trying to capture the dance in our playing. Singing the lines and trying to duplicate the sung inflections.
Analyzing structure or harmony to clarify meaning. Finding the places that reveal what the tempos and dynamics must be: the loudest and softest spots, the fastest and slowest. Playing the piece from beginning to end nonstop, to practice a performance.
These are good answers, and there are many more. Yet so often, when I ask myself what I’m doing, I have no good answer. I’ve succumbed to mindlessness! 
