There is no question that reading expands vocabulary, especially the reading of quality works. A GED teacher of 20 years noted that repeatedly her new students who read books always scored well on the vocabulary part of the entrance assessment test regardless of the grade at which they had dropped out of school. On the other hand, students who dropped out in 11th grade but did not like to read, consistently scored lower in Vocabulary.
Using a college-sized dictionary rather than going on-line to look up a word is helpful,too, because not only does one learn the new word, but he/she will spot other words on the page that are new and intriguing. Also, working with analogies is an excellent way to increase vocabulary. Taking a French course is, indeed, helpful since 60% of the words in English are derived from French (which is derived from Latin). Of course, taking Latin is helpful!