Last Saturday I found these books which can be very interesting to those of you who feel the need to learn more vocabulary or practice what you already know. They are small books, which is handy, and they are aimed at studying on your own. According to the publishing house: All the words have been chosen using the Cambridge International Corpus to ensure that students learn the most widely used vocabulary. Includes regular tests and helpful word lists.
There are six books, so have a look in any bookshop and choose the level you think it will be better for you. For my 1st and 2nd NI students I would recommend 3-4-5.
Try an exercise from the first booklet here on-line and an exercise from the second booklet here. (Sorry there aren’t examples from upper levels, this is what the official webpage offers at the moment).