Did you know that the most accurate predictor of earning power is literacy?  Literacy does not just mean being able to read, but also refers to your command of written language. I recently read an article by Steve Kaufmann at LingQ, a company that provides web-based language tutoring, you can improve your skills by copying a sample page from a source or article that interests you and pasting it into Google Documents.  You can find several readability indicators under File/Word Count, including the Automated Reader Index, which indicates the number of years of schooling required to understand a text.  Keep challenging yourself with harder and harder material until you are comfortable with content that is at an index of 12 or 15 or higher.

You should also measure the richness of your vocabulary.  Cut and paste a sample article into a web-based Vocabulary Profiler.  Using such a tool, you can see how many of the piece’s words are within the first 1000 most frequent words, how many are "academic" (AWL), and how many are “off-list.” Kaufmann recommends getting to the point where you are comfortable reading material that has 10 percent or more words in the AWL and the off-list categories. And don’t forget that you can use online dictionaries and word learning programs to increase your vocabulary.  When you come across a word that you don’t know, get into the habit of looking it up immediately.  I was doing this for a while, but then I got lazy.  Thanks to Kaufman’s article, though, I think I’ll try to pick it up again!