TOEIC

* "Very struggling" is incorrect. A better word to use for emphasis in this case would be "really."
* "Can't" is in the future tense, but you took (past tense) the test so you should say "couldn't."
As for my advice: like Norman said, it takes practice and time. Over time you will develop a better and better sense for how English sentences are structured, what a sentence is likely to be about, and what words are likely to follow. For instance, in the sentence "I took my dog for a walk" most native English speakers can guess (before they even finish reading) what the sentence will be as soon as they read "dog." It could be followed "to the veterinary" as well, but that's less common to see. Familiarity with the language also helps you guess when sentences are incorrect or incomplete. For instance "I dog walk park long" is entirely incorrect but you can guess they meant "I went for a long walk in the park with my dog" and most likely be correct.

In my case, I'm experiencing the same thing with Japanese, since I'm not very familiar with all the kanji and grammar structure yet, but speed improves with time as you get more familiar with the language.

Of course, just because it comes eventually doesn't mean you can't learn faster. Reading a lot of books and talking to people helps you develop conversational skills and also helps you get used to English grammar, sentence structure, and the ability to "fill in" or finish sentences before you've finished reading.