It can seem daunting to take this task on for yourself, but we promise that the work you put into understanding the grading system will also help you do better on your speaking and writing! :)
We recommend using some sample responses that show how different answers sound and look and then compare your answers to those samples. Start with referring to these official rubrics:
This should be your first point of reference no matter what, because this reflects the real scoring that will happen to your speech and writing. Using this together with other explanations and advice will really increase your scores.
The Speaking Section
Now that you've digested the rubrics, here are some sample responses to help you calibrate your speaking judgment: Sample Speaking Answers. There are also some official, ETS samples in these videos:
Carefully go through the samples above and apply what the speaking rubric says to the speech you hear here. Would you have scored these the same? What do you notice about different samples? Be extra observant and critical, because you're teaching yourself to properly evaluate TOEFL samples!
The Writing Section
Again, we have some official ETS sample responses here. There are a few more in those YouTube videos, too:
Just like with the speaking, be sure to slow yourself down and really analyze the writing presented and the factors mentioned on the rubrics. This is the same thought process a real TOEFL rater goes through, after all!
With those samples and the rubrics, together with the advice in Magoosh's explanations through your lessons and on the blog, your scoring of your own essays and spoken responses will be pretty accurate and you'll have a deep understanding of what the raters look for. :)