If you are an adult who does not need to study and go to school, you should consider why you want to learn a language. Setting a goal is the first important step in creating motivation. Having a clearly defined goal will help you persevere in your determination to master a foreign language. Why do you want to learn English? Which language skills - speaking, listening, writing, reading - are most important to you?
If you want to go abroad, especially for tourism, the emphasis should be on communicative language: understanding what others say and skilful communication. The language used in everyday situations is recommended: at the airport, in a hotel, while shopping or visiting the city. Generally speaking, your stock of words and phrases will be more important than learning advanced grammar structures.
If the English language is to be used for professional purposes, it is worth focusing on precision in the field of your specialization, learning the vocabulary and phrases that are often used in your work. For example, if you work as a waiter, it is helpful to learn about the words and phrases used in a restaurant by foreign customers. The basics of grammar are usually enough.
If you work in an office and your duties include writing e-mails in English, in addition to industry words and phrases, it is also worth learning about the rules of business correspondence, spelling and grammar rules. The boss is unlikely to be happy to discover that your work e-mail contains grammar errors.
If you would like to pass an English exam, proving that you know the language at a high level, you will not avoid the need to train every language skill: listening comprehension, reading comprehension, speaking, knowledge of grammar rules and the ability to write letters or essays.