A very common error is “it’s” and “its”. Remember,
Its is the possessive of it, denoting something that belongs to it, e.g.:
I like its style.
Jenny enjoyed the print-making course, appreciating its emphasis on learning the basics.
It is the only possessive that is not denoted by an apostrophe, i.e. “the dog’s” means “belonging to the dog”. But remember, for it there is no apostrophe: the possessive of it is its.
Even if you find this hard to remember, the good news for academic writing is that there is a simple solution: you should not use it’s in an essay because it is a contraction, and contractions are informal and therefore inappropriate in academic writing.