I think it is very important to understand the theory prior to sitting the exam. At least understand each of the topics covered. If you have a question you haven't seen before - without this knowledge, it may be difficult for you to answer the question.
I personally didn't get on with the AFE books (which I had purchased). I didn't like the style of writing, and did not appreciate their somewhat "large" format. I did however, enjoy Pooley's books which are the ones that I ended up using for my basic understanding (in addition to help from my instructors and other PPL students of course).
I then used an app available on both Android and Apple Store called "EASA PPL Exam" which at least at the time, had a tendency to have very similar questions to the ones I completed in my exam. Some were in fact identical to the ones I had seen in this app, whilst others were rather closely linked. This does give you a certain level of confidence prior to sitting the exams that you have learnt the right stuff and practiced similar questions to the ones you will have to face.
I would recommend AFTER having understood the topics read, and practiced the questions at the back of the book / end of each chapter which re-enforces the prior reading - to use an app with sample questions which are similar to the real ones is beneficial, and will guarantee your pass rates!
Hope this helps!
Alex