Good writing is clear writing. Do not use big words to impress. Do not try to write long sentences. Instead, try to explain your ideas as clearly as you can.
Be careful with big words
Big words tend to need very specific contexts (e.g. harmful vs. pernicious). They also often require appropriate styles and collocations. Generally, shorter words tend to be more natural.
Word repetition is fine
It’s fine, folks. Calm down. Don’t try to change the word “children” every time you need to use it in an essay. Children are children. They are not necessarily minor, or junior, or kids, or juveniles.
Avoid informal language
Do not use informal words and expressions like a lot of / lots of, a big fan of, kid, dad, mom, stuff, cool etc.
Leave a blank line between paragraph
This helps the examiner in reading your essay.
Do not use in a nutshell, first and foremost, last but not least etc. These are cliché.
Do not use contraction
Do not use contraction such as won’t and can’t. Write will not and cannot.
Do not use “you”
you; instead, use third-person words like people and (when relevant) young/old people, teenagers, workers, students, the public etc.