You can't really say one single method is better than all the other learning & practice methods, but if we were to pick just one way to continue improving your Korean, we would pick "writing in your journal in Korean every day."

Only diaries?
Of course this can be done not only in a journal but also on social media or in video format (e.g. on YouTube). The basic idea is that as long as you keep doing this regularly (ideally every day), you will quickly and naturally find words and grammar points that you do not know yet, and since journal entries are about your day-to-day life, you will become more curious to know these things than when you study with sample phrases in a book.

How do you start?
Just start by simply writing down whatever you can think of in Korean. Single-word entries are fine too. Gradually you will feel the want and need to form longer and more complete sentences as you spend more time thinking about things you want to say in Korean. It's quite simple.

What if I don't know a certain word or a grammar point?
You can easily look up words in online dictionaries (we recommend http://endic.naver.com ) and also look up grammar points and sentence patterns in our curriculum page ( http://talktomeinkorean.com/curriculum ).

Give it a try and you will love finding what you don't know and also the experience of being able to write things you couldn't before!