The most frequently used word in English is “the”. It accounts for about 7% of the ink. If you know only one word “the”, you can recognize 7% of the words in English. Of course, you can’t understand anything. But if you know 1,000 basic words, your comprehension is 72%. What happens if I know 2,000 basic words? Well, your comprehension will be increased to nearly 80%. The comprehension is 84% for 3,000 words, 89% for 5,000 words, 90% for 6,000 words, and 98% for 15,000 words.
How many words do you need to know? According to the information above, if you want to reach 90% comprehension, you need to know 6,000 common words. It is clear that we need to learn the most frequently used words first. If your goal is to study at an American university, actually the 2,000-word list plus AWL(Academic Word List of 570) can bring your academic text comprehension to 90%.
I do not recommed that you spend too much time studying vocabulary lists. You should spend some time, but not too much time there. Reading is the way to get familiar with the most frequently used words. Trying to memorize new words is boring, but reading is interesting. Read easy readers compiled for ESL learners.