If you can't already, master the basics of solving quadratics and factorising. This is pivotal for a level maths.
The main way for me was to (once all content was covered) do the past paper by topic questions off of physicsandmathstutor, focusing on my weak areas, then just hammering past papers. I did around 10 C1, 15 C2 and ZERO stats. My results? C1-87ums, C2-93ums, stats-45ums. So I'm gonna say my method works.
Not sure about new spec but this method should work providing that the specification isn't too different