Let's start with whether you need an error log. It is not mandatory by any means, but an error log is the single best way to dispassionately gather data about your own performance and pinpoint potential weak areas. If you make a digital one, you can sort specifically by question type or key words (yay technology!) and save it in the cloud so you can access it anywhere.
So how can you make an error log?
I did just mention a benefit of a digital error log, though we do like to recommend an old fashioned notebook instead. The act of writing something by hand really forces you to think more deeply. For every incorrectly answered question (on Magoosh and elsewhere!) you should write down the source, question number, question type, and the concepts being asked in the problem. These are your basic details that will help you notice patterns.
Next, write answers to some key questions:
- Why did you miss the question?
- Why was your answer wrong?
- Why was the correct answer correct?
- What will you do to avoid this next time around?
This document you create is not a one-and-done task. You should visit your error log often to review mistakes and errors before taking a test, to see if your mistakes are consistent or changing, and to track your progress. If you do this enough, by the time you sit for the actual test, you will be aware of your common errors and “silly” mistakes and you will work to avoid them or notice them when they happen. And that will help you find standardized test success! :D