One thing I've noticed in my time of teaching is that students tend to focus on their strengths of their field; they avoid their weak points. It's one of the greatest mistakes you can make when it comes to learning. When you work on your strengths, there's only so much room for improvement - and your training comes with diminishing returns. But when you work on your weaknesses you can improve your understanding significantly. Each little bit of learning yields results.
How do you define your weak points? Of course, you can measure them exactly. On standardized tests, for example, questions are often divided into categories. By checking how many questions are wrong in each category, you can get an idea of where your strengths and weaknesses are.
But there's a simpler, purer way of measuring your weaknesses: through emotions. Pay attention to what your gut is telling you. When I play classical piano, for example, there are tacts where I can feel myself tense up. Instinctively, I want to avoid them. Voila! This is a fantastic opportunity for improvement. Those are the sections I need to practice. The other parts of the piece need less attention.
When taking standardized tests, do you feel yourself sailing through analogies but freezing up during the reading comprehension sections? That's a blaring signal that you need to focus on reading comprehension for a while. By working on analogies, you might squeeze out a few more points. By working on reading comprehension, you've stumbled on a great opportunity to improve your score. Embrace it.
The same goes for any area of learning. If you're taking a calculus class and grasp the concept of limits - but arithmetic series are an issue for you - apply yourself to series for a while. If you enjoy engineering but struggle with visualizing things in 3-D, take some classes that will hone that skill.
Identifying a weakness is a cause for celebration. Don't fear it; think of it as a wonderful opportunity to learn.
Good luck and happy learning,