Source : https://elt.oup.com/student/practicegrammar/advanced/a_testzone/?cc=global&selLanguage=en
What I did : I did some grammar practices online
What I learnt : A lot of words seems very similar, but they are actually very different. Who and Whom, its and it's are some of the examples. The different tenses can also be hard to tell at times. Past and present tense is can be easily differentiated, but the harder ones, are past perfect and present perfect.