It's very important to have your own practice place. It can be your room, a special place in attic. It can be a corner of the living room. It's a place where you can easily prepare all the supplies for your practice session. Make sure you have your music stand, pencil, eraser, metronome nearby. And most important - be sure that this time is YOUR time. That means being unavailable for your family, friends and everybody else. Turn off your smartphone. Not just because somebody could call you. We are living in the digital world and often urge for checking messages and notifications can be disturbing for your concentration.
2. Keep your goals in mind!
Don't just wonder around in your musical world. Aimless practicing won't bring you any results. You have to keep always the goal in mind. Have a practice schedule! It's always reasonable to start with some warm-up exercises. Work on your tone first and then move on to scales, intervals and other technical exercises. You could also use the piece you have to study as a base for resolving technical difficulties.
If you're not sure how to schedule everything, ask your teacher for help!
It's not necessary to play everything over and over again. Sometimes it's wise to choose a little piece - a trouble spot - and try to work only on that. First you should try to understand what exactly makes it difficult for you and then find appropriate exercises to work on this problem. Are these large intervals? Are you running out of breath too soon? Are your fingers too slow? There are plenty of exercises for every kind of problem. After working on exercises try to replay your trouble spot. Do you notice any improvement?
4. Learn to play right, not wrong!
When you encounter a difficult bit of a piece it's more than important to learn it the right way. Impatience and fast playing can make a really nasty joke with our brain. If you play a difficult passage 30 times in row and make errors 28 of them your brain will learn to make errors. Our brains need the right information. Play as slow as you need to make EVERYTHING perfectly right. Every single time. And only when playing right comes naturally to you try accelerating a little bit.
You can use a practice chart to realize how much time you're exactly spending with your instrument. Also you should use a simple valuation system (of three stars for example) You'll soon notice that long practice hours don't have the desired effect on your playing if you're not practicing wisely. Or if you're really concentrated you can spend less time to learn more.