The easiest way to pick up a language is to learn it the way you learnt your mother tongue.
You don't have to give a second thought about how you say a sentence.
It just comes to you that naturally.
We blurt out things the way we have heard without thinking much.
We don't think about the grammar and the words or how they are placed.
We just know that right.
If you want to attain that kind of fluency in English you have to consult grammar book and learn the usage of words and where they should be placed in a sentence.
The foundations of grammar should be clear in our heads which word should be used with which word and which word suits at which place.
To know it just right one must take the help of grammar books.
Grammar books will help you develop the intuition of which word to use at which place.
A task that can be performed by practicing grammar exercises.
And then from this collection imitate the usages in context of the situation in which one is placed.
If you seriously read grammar books and take interest in sentence formation and word usages, very soon you would be doing it all on your own without any external help because you would have by then picked up the ways to go about sentence formation.
You would be easier with expressions and use newer words in sentences.
You will develop a sharp intuition as to what follows what and what happens next and what might be the next statement.
You will learn to figure out the correct and the more incorrect noises in English as you would in your mother tongue.
To acquire a fine and better understanding of how it all works, one must read ample number of statements placed in different topics and situations to gather the flow of it.
If grammar is learnt as a rulebook, there is a lesser chance that one would pick up correct usage.
It should naturally happen and one must understand why a certain word is used with a certain word and not with any other, and what things mean.
This is why grammar exercises and their practice is considered so important.
To start with, you should read the contents of any material in English given to you.
Let your mind focus on the key words or important words first.
It is these words which convey the basic meaning to you.
Also when your brain is concentrating on key words, you will be able to read faster because you understand the material better.
You know what you are reading.
To figure out the grammar part, scrutinize every sentence narrowly, learn the structure of its construction and what it attempts to convey to its readers.
Learn the differences in each sentence from the previous one.
Note well the interesting observations in change of structure of the sentences.
Learn the expressions and usage of words.
Reading is perhaps the easiest way to pick up any language, correctly and quickly.