Most of the learners want to be able to speak English and of course they want to understand what others say. So, they focus their learning time on speaking and listening. I can tell you that practicing only speaking and listening is wrong.
There are four skills that have to practice plus grammar, vocabulary, and I will add pronunciation although many people will include it in the vocabulary part. Reading and listening are receptive skills while speaking and writing are productive skills; that means after you listen or read a piece of text/song/etc you have to produce something in form of speech or writing.
Visual memory and reading are two things that help a lot when it comes to learning English. When you are reading you see the written words which helps you to remember how they are spelled which then helps you with pronunciation and of course at the end it helps you to remember the word. All these improve your vocabulary that is absolutely necessary in speaking and listening.
You have just learned new words related to your favorite topic. You have read an article on a website about that topic. Now it is time to produce something based on what you have learned. You would like to speak to someone about the topic you have just learned but there is nobody around to talk to. What should you do in this situation?
Writing is the answer! Write your thoughts related to the topic. Writing or typing on computer is a great way to cement your knowledge which again, means improving your English. Once you have finished writing your thoughts, it is very easy to reproduce them in speaking form. So, writing helps you with speaking because writing is speaking without voice.
Since it is writing, you are forced to think about grammar as well. Unlike speaking, writing allows you plenty of time for thinking. Thinking about what? About grammar! You will want to use good grammar in writing so you will try your best. Writing is the best way to review the whole grammar you have learned and actually apply it in a productive skill.
As long as you use the language, you learn the language. So, make sure you practice everyday all four skills plus grammar.