I struggle/d a bit with this. In general, I use way too many words, leading to accurate but convoluted responses. This makes it more difficult to be awarded marks, because assessors need to sift through unnecessary words.
Here is my advice. I hope that it will benefit you across a number of subjects.
Find a text. Any text of substance, really. And then summarise it.
And then summarise your summary.
And then summarise your summary of your summary.
And then summarise that again.
If you can end up having one or two sentences that clearly explains the contention and nature of a much longer text, you're going a long way to understanding it on a deep level. But more than that, you're learning how to say the same things in many fewer words. Being able to write concisely is an important skill, especially for a subject such as this one. In general, I have found that good summarising skills correlate nicely with concise writing skills.
Best of luck. Let us know how you fare.
