Have you visited www.freerice.com yet?
It is a vocabulary game (you are given a word and four possible meanings and asked to choose the right one) and a charity (for every correct answer, sponsors donate 20 grains of rice (recently increased from 10) to a United Nations agency. It is addictive.
The game is addictive because it is very good at calibrating your vocabulary and providing you with words that are just outside your comfort zone. Reports are that this is true for a wide variety of vocabulary levels.
My own background means I play the game at high levels (Shakespeare, Anglo Saxon and French all help). What intrigues me is how often I can "guess" the right answer for a word I don't know and have no memory of having ever seen before. It is possibly good practice for my vocabulary. It is definitely good practice for my experience of accessing information at the edge of my awareness.
Think about how often you "almost" know the solution to a problem. How useful would it be to be able to jump from "almost knowing" to having confidence in your "guess"?
Visit www.freerice.com. You can provide food to a hungry world while you learn to sharpen your sense of how to move from using what you know you know to using more of what know.