There are three broad reasons for losing points on physics exams:
1) Not understanding the concept
2) making mistakes
3) Getting stuck
The first one can be fixed by studying well, but many students don't do much for fixing the other two and are satisfied to stop at "I understand how to solve" . In physics, understanding only gets you started. In order to do well, you need to practice avoiding mistakes and getting unstuck (by yourself!)
Below are simple 3-step processes to eliminate mistakes and get unstuck.
3-step checking process to eliminate mistakes:
Always try to leave at least 10 minutes at the end of the exam to check your answers. Here's a simple process that I follow.
1) Mark them up:
As you solve the exam, keep marking questions that you are unsure about. These should be checked first after finishing up the test. Don't check questions right away as your thought process is still fresh in your memory preventing you from seeing the errors in them.
2) Hit the replay button:
Re-read the question and then follow along the entire solution to make sure nothing is missing. I promise you that this step will be boring, but you have to check everything because mistakes can be anywhere. It should also not take much time as you are just (actively) reading through something that you have already solved.
3) Test your answer:
Almost all answers start with an equation. Plug your final answer(s) into the starting equation and see if they're valid.
3-step process to get unstuck:
1) Write everything down first:
Write down what you know before trying to figure it out. Many students, when they realize that they will get stuck after a few steps, stop and try to think about that step in their head. When my students get stuck during a session and ask me for help, I always tell them, "Write down everything you know first", and most the time, they figure it out by themselves!
The reason that you stop writing early - before getting stuck - is that knowing you will get stuck later makes you doubt what you are writing now. Don't listen to that fear, and keep writing; you can always cross it off. But once you write it down, your thinking will be much clearer.
2) Go back to the question for clues:
Read the question again, especially to see if there's a piece of information that you didn't use in the solution
3) Think of formulas:
Recall any formulae that involve this piece of information and can be used.
But remember, the first time that you use these processes shouldn't be on the test. They are skills to be mastered, not straightforward concepts to be learned. You need to practice using these processes while studying. This is discussed in more detail in my other article "The most important part of exam preparation that no one does"