To improve your grammar in writing, those grammar books do help.

I wholly agree with the point that self-confidence is vital in this sense.
I am not able to speak Cantonese fluently, my friend would certainly laugh at me for my poor Cantonese.

Yet, there was once I met some new friends in a camp,
most of them spoke in Cantonese, no one knew me there,
so I brought up my courage to speak in Cantonese with them.
Surprisingly, I could speak very fluently.
After a few days I told them that I was not a Cantonese and
cant speak fluently either, all of them looked at me surprisingly, feeling that's impossible as I was able to converse fluent Cantonese with them.

That's the thing, self-confidence.
Do not have the mindset that you are lousy in certain language
and lose your courage.
No one knows whether you can speak it fluently except yourself.
Just pull up your socks and speak it out !

Btw, I still do not have the courage to speak Cantonese with my close friends. ><
Sorry to be so contradicting but it's a personal experience. lolz

Real World Issues may help actually