TOEIC
Currently I'm very struggling with reading English sentences fast. The other day, I took an English test called "TOEIC" and I got a score of 750/990. There are 2 sections: which are Listening and Reading, and each section has is worth 495 points. My listening score was 440/495, which is ok so far, but my reading score was 310/495. I think the problem so far is that I can't read English really fast so I can't couldn't finish whole of the whole reading section. My understanding ability isn't that bad, but because of my reading speed, I can't get more scores a higher score. If you have any advice for fast-reading, please let me know.* "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.