how to improve the fluency

grammar doesn't help about it.

speak as much as you can. when you speak and something you are not able to express, remember it, than look up at the dictionary, use google for help and repeat it in order to avoid making the erro again.

record yourself when you try to explain something like:
- plot of a movie you have seen
- how something-that-you-know works (computer, turn on heater...)