Here are a few tips to help your music practice (or any other practice, for that matter) become more efficient and helpful, rather than discouraging and upsetting.
Slow down
When you’re learning, it takes time for your brain and body to synchronize. Give plenty of space for synchronization to happen by taking things very, very slowly to start out. There is no such thing as too slow when you’re learning skill, technique, or piece.
Give yourself frequent breaks
It’s much better to learn something in three, highly-focused 15-minute sessions than one long, unfocused 45-minute session. If you’ve been at it for a while, either walk away or put it down and switch to something else.
Sleep on it
If you’re having a particularly difficult time and it seems like no matter what you do you can’t get it right, you may need to come back to it tomorrow. When you sleep, your brain processes everything that happened during the day and prunes away necessary information. Sometimes all we need to do is sleep to let our brain catch up.
Switch it up
Don’t always start in the same place (aka the beginning). Try starting in the middle or near the end of the piece. It will help you pay more attention to those bits later on that tend to give us more trouble than the beginning.
Be forgiving
Learning anything is hard work! Don’t be too hard on yourself, it only makes it worse. If something isn’t working, use the tips above to help diagnose the problem. Worse comes to worse, bring it to your teacher at your next lesson. But I guarantee that if you follow the advice above, it probably won’t come to that!