Just buy yourself a book or dvd if you prefer of driving theory practice. When i did it (it was 4 years ago now so might be slightly different) the book had about 1000 possible questions that you could be asked, so just memorise that and its all good. FYI a lot of the questions are common sense, and a lot overlap each other so there isnt as much to learn as you might fear. The test is 50 multiple choice questions (with 1, 2 or 3 possible answers to be selected), and you have to get something like 47 right to pass.
I believe you can do hazard perception example tests online, else a DVD might be a good purchase. The hazard perception itself consists of a few short video clips and you click the mouse every time you see a hazard (eg someone trying to cross the road). The key is to click when you first see the hazard, and then when someone changes (eg. that someone now steps out into the road). However if you click too many times on one particular clip, you will get zero points.. so theres a balance to be found - basically they are looking for people who are confident with spotting hazards rather than fearing everything/nothing.