It is important to master grammar gradually and to try using it (whether by exercises or by corresponding yourself with other speakers). As for vocabulary, it's better to learn it in context and not by memorizing lists and lists of words. Reading and listening to material of that language helps. If you practice regularly, you'll learn better.

oooh.....too big and global question. reading,speaking,grammar,understanding... And in every part of education you should practice and learn a lot

Things you must do to improve your English: - Speak clearly, concisely and use simple vocabulary. - Listen, carefully, to English movies or speakers. Take note of the words/terms used and read them over and over till you start using them effectively. - Read aloud and talk to yourself loudly in English to see how well you are doing. - Watch English movies with English subtitles on. This will allow you to compare the written words to the correct pronunciations. - Listen to English songs. This will help you a lot. If you can’t understand the accent, take the lyrics which you can get by searching at google. - Avoid thinking in your mother tongue, translating it then saying it in English. If you want to speak fluently, you will have to "think" in English. - Communicate with native speakers and try to imitate them to learn how to speak correctly and how to pronounce the words correctly. This way also can help your vocabulary. - Write sentences and essays which include new interesting vocabulary. This can help you improve both your speaking and writing skills. It also helps you remember the new words that you acquire. - Read as much as possible from a different variety of authentic reading materials (books, newspapers, magazines, etc). - Use a good English dictionary that can clearly define words, provide information about grammar and give sample sentences to show how words are used in context. Good Luck!