Most exam answers are quite short. The trick is to approach the question correctly from the start.
Algebra errors are quite costly. They can be avoided by slowing down, writing carefully, and checking your algebra from time to time.
Read the question carefully. I often grade answers that clearly overlooked a piece of information that was given in the question.
Don’t panic when an answer does not come together. Move on to the next question and come back to the one that bugs you later.
Explain your answers
Just giving me a graph and letting me figure out the answer does not work.
When you draw a graph, explain why you think the curves slope up or down, etc. If you make a mistake, at least I can give you partial credit.
Make room. A lot of answers are very crowded. Then you find that you have to fit something else in and soon you have a mess on the page, where I don’t even know in what order I am supposed to read things.