There's no magic bullet for mastering a complicated piece of music when you're practicing piano. Instead, develop good piano practice habits and your work will speak for itself.
You can crunch the numbers to find the secret to mastering a musical instrument, but ultimately, it all comes down to blood, sweat, and tears. That's not to say that there's nothing you can do to make your practice more effective and efficient.
When you don't have endless time to spare, every minute counts, and getting more out of your practice sessions can make all the difference. For example, make sure to sit down and practice right after your lesson—that way, you can implement any advice and techniques that your teacher suggests while it's still fresh in your memory.
Another useful tip is to keep music present in your life, even when you don't get the chance to practice. For example, listening to different recordings of the pieces you're working on in the car or during your commute, to inspire you and help keep get the piece into your head. Ultimately, there's no substitute for regular, dedicated practice—but you can always practice smarter.