Nord 121 goes a long way in explaining what is required.
What makes the whole process smoother is the right acedemic background from school. In the UK, maths, physics, english are the critical subjects for 'O' level/GCSE/NAT 5 where you achieve at least the middle pass grades. Add to that 'A' levels/ Highers were you are demonstrating an adequate amount of grey matter.
And above all ~ an absolute passion to fly. As one teacher called it "plane daft".
Demonstrate that you are a team player is also an essential ingredient. Those with a good golf handicap will find flying straightforward.