Below are three links that I found which I consider interesting and useful for expanding shorthand vocabulary. They refer to word lists that are either common in English reader texts (General Service List), or in academic texts (University Word List and Academic Word List). Some of these lists have exercises with passages that employ the words, and are good for dictation practice (Academic Word List Exercises). It is a good practice to go over these words in shorthand so that there's no hesitation in writing them in dictation. The challenge is to write the words as fast as possible.
If there is interest, I will make the lists downloadable as well.