Since I have to create grammar rules, I thought it smart to improve on my English grammar skills (which are subimpressive). So I bought the book "Essential English Grammar" by Philip Gucker. About 150 pages, including exercies. And it's sweet. It even says so on the cover :) "All the grammar really needed for speech and comprehension, without trivia or archaic material, clearly presented with many shortcuts, timesavers... selfstudy or class use, for a beginner, as a refresher... an ideal supplement to phrase study... the most efficient system for adults with limited learning time". Really digging this.