You should try different methods and see which one works for you. It is individual, some people can learn language by themselves while some need a teacher to guide them. It also depends on what aspect of the language you need to learn (grammar, vocabulary, speaking or writing, or maybe all of them) and your current level. If you need English for your job, maybe there are some standard terms and phrases that are used in your field. You can start by learning those. But I think it won't get you very far. You need good foundation, you need to be able to talk on daily topics as well. You can practice speaking with a language partner or a teacher, and use a text book to study grammar. For example, one of the greatest books for learning English grammar is "Grammar in Use" by Raymond Murphy. You learn follow this book and then practice what you have learnt in your speech. This approach is quite boring though... If you are a fan of books, you can try reading in English. Reading will help you to learn new words and the way they are used in context. But personally I don't really like reading. I watched a lot of TV series in English. It was difficult at first. Sometimes I had to pause the video many times and go back. After a few episodes, the words started to repeat and it had become much easier to understand. You just have to really make yourself watch it, even if now you only understand 50%, gradually over time it will go up to 100%.