If you're getting 19, I assume you probably miss 0-2 problems on the sections you "nail" and probably miss somewhere between 4-8 on angles. I would check out the small mistakes that you make on the ones you typically nail, learn to recognize how to do those problems so that when you are faced with them again you will know how to approach them.
For me what lowered my score in the beginning was cube counting. If you are getting less than 15, I would try to be more disciplined in counting (practice is important for this because recognition becomes easier with each subsequent test).
Angles are really difficult, no doubt about that. My technique is to eliminate the obvious wrong answers. Then look very closely at the actual angles when the laptop technique doesn't work. Get very close to the screen to the point that the pixels help in letting you know how big the angle you are looking at is relative to the one you are questioning. You might have to go back and forth between the two angles to compare them.
For example lets say you have the choices
A) 4-3-1-2
B) 4-2-3-1
C) 3-4-2-1
D) 4-3-2-1
Step 1: You compare 1 to 2, and you determine that 1>2 so you cross A off. If its the other way around (this happens every once in a while but not too often), double check that you're sure this is the case because if it is then that is your answer and you won't need to look at the other answers.
Step 2: Compare 4 to 3. If 4>3 then C is your answer and you are done. If 3>4 then you have two answer choices left - B&D. The difference b/w B & D is that one says 3>2, the other says 2>3. I would then implement the "looking very closely" technique to determine your answer.
Notice that along every step of the way there is a possibility that you will judge the angle wrong and that is something that is almost impossible to alleviate. Wish you the best and I hope this helps....