practise, the more you do them the more you realise how the questions can ask the same thing over and over just with different buzzwords for the rubric and the themes. also the key to short answer is bsing your answer if you don't understand what the text is about - the best thing about short answers is that you can just take the most surface-level idea or analysis and as long as you have quotes and techniques with 'analysis' that you can just bs a link back to the ideas of the question, that grabs you the marks even if you have no idea what the text is about
the one that's stuck with me the most is a 20/20 exemplar i remember seeing ages ago where the q was 'how does the text show winter in [place]?' and the answer the student wrote was 'they show winter by saying what you can do in it'. it's a very simple topic sentence and idea but since it answers the idea it gets the mark and it made me realise that you have to oversimplify your mindset because in essays you're expected to have complex sophisticated ideas and you need to dumb yourself down for short answer
i agree with all of this, plus i would suggest maybe looking through the content and syllabus for the modules being tested (just look at the kinds of words and phrases being used). the reason why is bc the short answer is sometimes related to the things they are assessing in your essays as well, but more indirectly, and you an always recycle the type of logic you use in an essay for the short answer.
for example in english advanced this term there is an emphasis on storytelling and challenging worlds in my school and that is what will show up on my essay. if we had short answer id assume that if i got a piece of art/poem or smth like that, that it relates to storytelling in some way. storytelling can refer to the type of techniques they are using, and how they convey their message etc, and obv this translates across to all art. so i can essentially receyle the thesis i might use in an essay on my short answer too. obv not word for word but just the ideas.
this is just smth to think about, if your short answers have nothing to do with your essay stuff ignore this