In order to improve your proficiency in any language, you'll have to work on "comprehension" and "expressing yourself" in that language. Comprehension includes reading and listening while expressing onself includes writing and speaking. 
In my opinion the crucial point in learning a language is to find a way to make learning this language a positive experience. So my advice would be to find something that you enjoy doing, e.g. listening to music, reading a book, watching videos on youtube etc. Maybe even write a diary in German if this is something you like to do. Finally  you'll have to practise speaking, so you can visit the country, do a tandem language exchange, or take lesson with a native speaker, whatever suits you best.
I hope this is helpful to you!

There is no one-fits-all method. Everyone has different learning styles and needs. I like to study languages via writing and speaking. I get bored with textbooks and also like to listen to podcasts for natives from the start rather than for learners. I don't need a teacher spoon feed me because I'm an adult and can think for myself. What I expect from a teacher is feedback and a little bit of guidance. But I'm responsible for my own learning process.