IMHO, the far most important thing to do is to listen. I prefer podcasts, but anything (radio, films, TV, overheard conversations in bars) will do.
Understanding spoken language is also (again in my opinion) by far the most difficult part of learning a language. Especially in real life, and really noisy, situations, where you probably only hear half of the sounds people are making. The rest you will have to fill in yourself - which is sort of like solving crossword puzzles in real time.
This takes a lot of practice, and there's really no way around that.
Starting by studying all the rules of formal grammar is, I think, a bit like learning to play tennis by first studying the rule book a couple of years...