If you speak Russian, some English grammar rules will feel natural and others will feel confusing. These are the biggest differences to focus on first.
Russian word order is flexible because grammatical cases show the role of each word. English has strict SVO order because word position determines meaning. 'I love Maria' and 'Maria love I' mean the same in Russian but are very different in English.
Russian has no articles at all. Definiteness is expressed through context, word order, and intonation. English articles 'a', 'an', and 'the' must be learned from scratch with no Russian equivalent to map onto.
Russian has two aspects for every verb โ perfective (completed action) and imperfective (ongoing or repeated action). English has nothing equivalent. Russian speakers must instead learn to use English tenses to express this distinction.