Have you had an experience where though you could understand what a Japanese was talking to you in Japanese language, you could not answer back in Japanese? I can say that speaking and writing is not focused in most language classes, as there are no speaking section in JLPT... but you may want to learn Japanese not just for JLPT. Hence, I hope you can improve every skills of the language including speaking. It's really good practice for speaking by writing something in Japanese. We can speak what we can write. When you can write well, you will be able to speak well, too. And to understand grammar clearly by your own language, it's also effective to practise writing. You might understand the difference of expressions between the two languages.
So how do you practice?
I recommend writing emails and keeping a diary. It might be a bit difficult for new learners to have a chance to send emails to Japanese, but you don't need anyone else when you keep a diary.
To do this, you may want to consider using にほんご日記. At first, part of each section in this book introduces some sentence patterns and vocabularies, and after that you practice to keep a diary by those expressions. Though the grammar might seem easy, I think to write something by the grammar is challenging at first.
The level of the grammar in this book is around JLPT N3.