Past paper exam questions can offer a great deal of learning if approached correctly, both in terms of understanding and exam technique.
This post will go through the resources you need to make the most of an exam question and also the approach you should take to be able to ace that exam question.
Obviously, you need the question itself.
Next, you need the mark scheme. This may sound obvious, but you won't get the most of a question if you do it without knowing if it is right or wrong - or how right or wrong it is. For this reason, most textbook questions are useless for revision - not because they are bad questions, but because you cannot check if they are right or wrong.
However, there are plenty of workbooks to buy with answers included and also websites where questions and answers are provided, such as Physics and Maths tutor (which does more than physics and maths and is free).
There is also My GCSE science (which has questions that are specific to the 2015 AQA, Edexcel or OCR GCSE specification, including revision videos and multiple choice questions, but costs about £25 for double and £ 50 for triple). You can try their trial videos and whether you buy or not, you should also follow their blog full of useful advice.
Finally, if you are using a past paper, then it will come with examiners' notes. These are treasure troves detailing other peoples' mistakes with the exam question which is great for you, because if there's one thing better than learning from your mistakes, it's learning from other peoples' mistakes. For this reason, past paper questions are the most useful questions to practise.