Repetition is the key to learning a tough spot in your piece of music...except repetition can be boring!
It's NOT BORING when you make it interesting. It turns from boring to ENGAGING. How do you make it interesting?
First.... rarely play the whole song when you are practicing. It's too much NEWNESS for your brain to take in. Dive in and find the tough spots. Now start your repetition woodshedding. Select 2-4 bars (no more!) and vary it.
Play it LOUD, play it soft, play it fast, play it s l o w, play it sta-cca-to, play it legato. Invent your own ways that keep you focused. Now find the next tough spot and do the same.
Finally, repeat these short passages daily as part of your warm-up. One day won't do it but 3-7 days surely will. Wouldn't it be great if learning the piece was as much fun as playing it? With varied repetition it will be!