The next fast typing lessons will be about typing common words on the keyboard. Why are these words in the lessons? Because they are most common in a given language, so by practicing typing on these words, you program your muscles so that they can type a given word quickly and without errors. This is similar to fast reading, or rather global reading. In this technique you do not focus on individual letters, but looking at the word you know its meaning. Your muscles will remember the keys sequence needed to form a word.
Take English for example. It is estimated that we have over 170,000 words in English. As a rule, a native speaker in a given language uses between 15,000 and 20,000 word families. A variation of a given word can be modified by tenses, in some languages by modes, cases, or persons is counted as one word, therefore it belongs to the same family. The truth is, language learners who learn for a long period of time know only 2-3000 word families. Research shows that in order to speak a language effectively, you need to know about a thousand families of words that are most common in a given language. Knowledge of eight hundred words gives a spoken language understanding of 75%.
So practicing touch typing of the eight hundred most common words in English, will help you practice 75% of the vocabulary that is commonly used.
AgileFingers contains about 2000 words in keyboard lessons, so all you have to do is practice. However, as mentioned before, typing texts is more interesting. It also practices the most common words, because the words also appear with some frequency in the text, and the more popular ones will necessarily occur more often.