You don’t have to be a grammar whiz to enroll in a TEFL course…but if you’d like to brush up your skills anyway, try:
- Grammar In Use — Available in different levels, this reference book is useful for your own reference, especially for examples of tenses, and also has photocopiable exercises for students (to be given out mainly as a last resort in class or as homework; they are useful for practicing grammar but a bit dry and not particularly communicative). It’s quite well organized and so easy to find what you’re looking for. I picked up a slightly older edition in a discount bookstore in the US for $4.99. Grammar doesn’t change that much. Even full price, though, it’s a good investment.
- Practical English Usage — This is a good reference, especially for more advanced grammar points, and is arranged alphabetically by topic (slang under “s” just before swear words and tenses). The downside is that its size and weight make it hard to lug around in a suitcase or backpack along with everything else. Overall though, worth the price and extra exertion required to carry it.
- The “Dummies” series is usually a crowd-pleaser.
- Also consider Grammar For English Language Teachers and Painless Grammar. You can start from the basics in this book (because it’s geared towards middle and high school students…but don’t think about that).