avoid reading the book from end to end.
Do a mock test first, note down all the ish you don't know and then guess, all the stuff you didn't know study and memories them using highway code book, then do another test, follow this procedure several times a day, for maybe 2-5 days and you should be ok.
one thing though, the stuff you know, you need to do lots of test and that repetition is important because during the theory test you might panic so you need to have that extra confidence.
hope this helps.