how can I get the fluency of english???

I strongly doubt when I can be a good english speaker...

Now I am thinking that, just because I usually can't give back exact replies to native speakers of english quickly
when they suddenly talk to me.

if I had more 30 seconds, I could reply better answer to them....
I should have said like that...

I always feel depressed like that whenever some strangers talk to me in the town.

I'm sure exercise of speaking foreign language is similar about muscle training.
It means that takes very long time to achieve the goal...

But I need intense. I can't wait it anymore.
ah..... how can I do ???