No matter how hard we try to practice something perfectly, we're always going to run into challenges and we're always going to make mistakes. Getting through these challenges (trouble spots) can be very time consuming and may seem almost impossible to overcome if you don't approach them the right way.
Let's take a look at the "wrong" way first:
1) You start playing through a phrase of music and run into trouble spot.
2) Despite the mistake or difficulty you play though the trouble spot to the end of the phrase.
3) You run through the trouble spot about 10 times.
4) On the 11th try you finally get it right and move on to the next phrase.
What you've just done is played the phrase wrong 10 times and right only once. This is the equivalent of having played it 10 times wrong and 0 times right. If this sounds familiar, then your practice method needs to change ASAP. You want to be playing you phrased more times correctly than incorrectly.
Here's the correct approach:
1) Find your trouble spot.
2) Expand your trouble spot to include a few notes before and after it.
3) Play through the spot as SLOWLY, PRECISELY, and as RELAXED as possible so that you are able to play each note 100% correctly. FORGET ABOUT TEMPO!
4) Stop, drop your hands, relax, and count 2-5 seconds.
5) Repeat the phrase again in the same manner.
6) Repeat 1-5 about 5-10 times CORRECTLY.
7) If you're doing it right, the phrase will start to feel a bit easier. This is when you can add A LITTLE BIT of tempo and start at step 1 again.
If you still make a mistake, then you have to add in a "scientific method" into your practice:
1) WHERE: Ask yourself where EXACTLY is the mistake occurring in the trouble spot phrase (e.g., on which notes is the mistake happening).
2) WHAT: What is the mistake? Are you getting a dead note? Buzzing? Flam? Can't reach?
2) WHY: Why is the mistake occurring. Are you too far from the fret? Is your elbow not out far enough? Are your hands relaxed enough? Are you setting up the next note by hovering early enough? Do you need to lean left or forward more? Etc.
3) HOW: Once you think you've found the culprit, develop a solution to fix it and try it out.
4) If your solution doesn't work, try something else. You shouldn't have to run through more than 5 possible solutions to any problem.
Finally, you need to know that this method works VERY WELL. You may not feel immediate progress, but if you're following the steps above and follow them consistently, you will overcome your trouble spot soon than you think.