Hint: It’s not how much; it’s how.
How Long should I Practice? 
Beginners should try for 10 minutes. Intermediate students can choose but at least 30 minutes. No-one should sit at the piano more than 40 minutes without taking a break which means getting up, having some water, looking outside (2-5 minutes). 30 minutes could be broken into two lots of 15 if that is what you like. Advanced students should be doing 60-80 minutes if they really want to progress.
The Key… 
…is daily – it is better to do less if time has run out than to miss a day. Of course life can intervene but progress only comes with daily practice. Why do coaches want their teams working out every day?
When to practice? 
This depends on your family circumstances, where your piano is situated, or if it is digital, can you use headphones. Mozart practiced either very early or very late. I always prefer early. But practicing at the same time every day is really helpful in maintaining regular practice.
Remove distractions! 
.
Turn off phones and devices, leave social media for later, keep the cat and dog further away unless your playing makes them go to sleep.
Warm up.
At least 5 minutes for intermediate students and 10 for advanced. Hanon exercises, scales, dozen a day, and at the end maybe you have a piece you always play hopefully from memory. In a half hour lesson I cannot always go over your exercises but once learned, I expect you to play them for warming up.
Plan your practice.
For intermediate but especially advanced students, after warming up you should work on a 4-6 measure section that presents you with difficulty. This is how my student Chelsea practiced, 4 measures at a time, memorizing as she went. Quinn was the same. Once you have mastered that section (and that might be your whole practice depending on difficulty), move on to another 4 -6 measures. Then try connecting these sections if they are adjacent.
BIGGEST MISTAKE
Always starting over from the beginning
It feels natural to start at the beginning, so many of us play from here, try adding a few new notes, make a mistake, then start again from the beginning. You waste a lot of time playing this first section over and over, while you could be learning new sections or correcting mistakes. Instead, focus on a new part and practice it alone. Only combine it with the previous sections when you get it right, then move on.
Right, left, together.
Learn right hand and memorize, learn left hand and memorize, then play both hands and memorize. Three different tasks. They all need separate attention.
Of course you can play all of your piece at the end of the day/week BUT not at the beginning of your practice when you are least tired and most focussed.
Ask me for more detailed specific plans for your particular pieces.
