What you say is important—but so is how you say it. If you find yourself using the same words over and over again, making embarrassing mistakes in grammar, or misspelling and mispronouncing words of average difficulty, you may be hurting your chances for success in school or on the job—without even knowing it!
If you’re not satisfied with what your English says about you, test your problem areas with this popular, remarkably effective handbook. Each of the thirty short chapters zeroes in on a different aspect of grammar, usage, spelling, and pronunciation, with challenging and often amusing exercises to help you monitor your daily progress. Your vital communication skills can improve dramatically, in just fifteen minutes a day, with Thirty Days to Better English .
It is not as good as Word Power Made Easy by the same author, but can recommend to someone who really wants to improve his/her vocabulary in a short period of time.
This is a good book for understanding a few common grammatical mistakes and a quick assessment of your English. There are parts of it, such as section on spellings, which is irrelevant to most people in the modern world(because of prevalence of spell checkers and auto correct). I didn't find the pronounciation part accurate when compared to online dictionaries. And for improving vocabulary, you are better off with word power made easy.
If English is not your primary language and you expect this book to help you speak conversational English, my suggestion is to start from the basics, how to construct simple sentences and compound sentences, because this book doesn't teach that. This book is great for improving your grammar, pronunciation, and spelling, preparing you to speak confidently in public.