There’s no one answer that works for everyone. Otherwise, you could just google it. Actually, you probably can google it, but the answers will be nonsense. People always seek answers, but you need to ask the right questions first. What’s your career? Why “three” languages? If it’s about budgeting your time and energy, I’d suggest that if you already know Persian and English, you can learn three Indo-European languages in the time it would take to learn a non-Indo-European language such as Chinese. Over a billion people speak Chinese, but you might be better off learning Spanish, Portuguese, French, and German in around the same amount of time. Honestly, though, if you’re only learning a language for your career, it’s going to be hard. Out of curiosity, what was your experience learning English — did you enjoy it?