There are a number of mistakes made when speaking or writing English. Listed are some of the common mistakes made. Some Common English Grammar Mistakes 1) Present and Past Tense. ... 2) How To Avoid the Overuse of Adverbs. ... 3) Your/You're. ... 4) Misplacing Apostrophes. ... 5) There / Their /They're. ... 6) Confusing similar spellings and words. ... 7) Using incomplete comparisons. ... 8) Getting adjectives and adverbs confused.