If you speak Tamil, some English grammar rules will feel natural and others will feel confusing. These are the biggest differences to focus on first.
Tamil is SOV — every sentence ends with the verb. 'Naan padam paarkiren' literally means 'I film watching-am'. English requires SVO — 'I am watching a film'. Tamil speakers must completely restructure every sentence.
Tamil has no articles whatsoever. Definiteness is conveyed through context and demonstratives. English uses 'a', 'an', and 'the' — concepts that Tamil speakers must build from scratch.
Tamil verbs encode the gender and social status of the subject. Tamil also has separate verb forms for polite and informal situations. English verbs have no gender, no social encoding, and only minimal conjugation.