Practice and best guess predicted papers for GCSE Maths, expanding to the new GCSE soon.
It's important to note that any predicted paper from any website is logical and systematic guess work at best and may not be the topics which come up on the actual exam. However, teachers have used their judgement in creating these papers from previous 'typical' topics and also through the process of elimination from paper 1. This is not to say if a topic came up on paper 1 that it can't come up on paper 2 in a different form.
For example standard form was presented as a compare on paper 1 2018 AQA. This doesn't mean it won't appear on paper 2. You may be asked to carry out a calculation