Just a shout out to anyone thinking of giving their theory test for car or otherwise, apart from reading through the highway code which is comprehensive enough, you should have a look at this website,
they have really good mock test, give them again and again, practice. But when you get an answer right the best thing to do is not to just say okay that is the answer to this question and thats it, read up why it is so. This gives you more of a scope for similarly related questions.
There are other websites as well, but in my view this website is very comprehensive, if you know of better ones, post it over here.