As with any form of performance, slow and steady is the way to success. If you want to become fit, it doesn't help spending one intensive week at the gym and then doing nothing. A consistent effort over a dedicated time is required. Once you've reached your fitness goals, you cannot simply stop working out. You need to keep practicing regularly. The same goes for language. It doesn't help to work with an English teacher inconsistently and expect to become a fluent speaker and writer.  

Speaking and writing in English are performance activities. Every time you write or speak, you are performing to an audience with communicative goals in mind. Confidence in your voice is developed over time and with practice. There are many guided performance activities which you can do to strengthen your confidence, fluency and accuracy.  

At some point in your English learning journey, you tend to become complacent. Bad habits fossilize and you give up on improving beyond your communicative abilities. If you want to reach an advanced level, sitting in your comfort zone is not going to get you there. It's on you to observe your mistakes and correct them. This takes effort to memorize, drill and perform the better versions.