I wanted to improve my reading vocabulary, so I went through a small dictionary and underlined all the words I didn't know the meaning of. I then marked all these words in my larger "breeze block" dictionary and memorized the definitions using various memory systems. There were about 1500 words and I'm continuing to learn more.
I think there would be an easier way to do this exercise using Wordcount. Wordcount presents the 86,800 most frequently used English words, ranked in order of commonness. With this listing of words in order of commonness, it is thus easier to decide which words you need to learn as a priority.
To aid this process, Wordcount could introduce a feature where a brief definition of a word is given whenever you hover the cursor over a word. To get a more in-depth definition (or perhaps a link to an online dictionary definition) there could also be an option to click on the word.