Style means choosing the right word(s) for the audience.

If you are required to write in a semi-formal / neutral style, you should avoid using too many phrasal verbs, avoid exclamation marks (!), contractions (don’t, can’t, it’s), smiley faces (J), slang (wanna, gonna), “chat” words (u instead of you, 2 instead of to) and abbreviations (info, advert, e.g.). In IELTS, it is acceptable to use the first person (I). Connotations are also an important element of style ("precise").