(Tangent: Why did my Spanish teachers tell me that it's "doblar a la izquierda" when in Spain it's unequivocally girar? Ugh.)
Once you get through that rough patch, you will absorb the language like a sponge, depending obviously on how much you immerse yourself into it. If you listen to and read a language all day, before you know it you will find new words and phrases sneaking their way into your speech.
The part that comes next is more challenging, and it's where I find myself now. There will be a point at which your vocabulary and grammar will be sufficient to communicate nearly anything you want to. There will still be plenty you don't know, but using what you do know you can describe your way around the gaps in your knowledge. The phrases you put together might not be quite how a native speaker would say something, but you easily get your point across. If any of the above applies to you, congratulations, you've reached the language learning plateau.
In order to improve from this plateau, you need to make a concerted effort to fill in those gaps, take every opportunity to listen to native speakers and read in the language. This is my latest project, which I am going about in a variety of ways.
First, and I am ashamed to admit I haven't done this until now, I am reading in Spanish. Not just skimming through a newspaper each morning, but tackling a book.
Second, writing down all new vocabulary I come across, and then actually studying it! This notebook and my pocket dictionary come with me everywhere.