Do you know what the most frequent word in English is? What about the most used verb? And the 50th most common word? Now you can check, not only that, but all the 5000 most used words, for free. Access http://www.wordfrequency.info/free and download the list.
More than just out of curiosity, the list can help you select wich words you should memorize, as they are more used by native speakers.