Every word that you stroke must be clear enough to be correctly read. Perfection is not necessary, but be tough when you grade your work.
That's it. Those are the only rules for the Magic Drills. Write clearly at all times, and write at least two of the four words in each sentence.
By the way, those are also the only rules that you need to succeed at stenography. If you can write good clean strokes, and if you always write at least two out of every four words, then you won't drop many words on your test..