Whichever “flavour” of English you’re studying, you will be assessed on your own writing ability at some point (if not in every paper).  So-called “basic errors” will cost you marks and often give examiners a poor image of you.  Particularly nasty ones are:
Improper apostrophe usage
Confusing homophones

You should also always try to organise your thoughts to allow you to write in a logical, structured way.  It is ALWAYS worth planning before you write, if only to allow your writing a logical shape.  If you know where you’re going with your argument from the beginning, your examiner is more likely to see this from the start and follow you better.  An essay or analysis which skips about and seems to contradict itself rarely impresses.

Remember to organise your writing into paragraphs by topic.  We do not like reading whole-page paragraphs.  They are hard on the eyes and suggest a lack of organisation.  Shorter paragraphs are fine, if they cover a single topic in your essay/analysis.

What we also don’t want to read is randomly started paragraphs that actually continue from the previous one.  See what I mean? ;-)

Writing Accurately