For IOT, just get fitter. That is all.
Re GR4s, don't bother doing anything before you go (unless they send you the maths package they always used to - even then, I gave it a stiff ignoring and did just fine on the course...), as it won't really help that much. On WSO school, just work as hard as you can, listen, learn and then work harder. Whether you make it to GR4s after all that hard work will then rely on your natural aptitude and you won't be leaving it to chance.
So,in summary, go running now and then continue to enjoy your life as it is, without bogging yourself down doing sums. You'll have plenty of opportunity to practice sums on the course and get to the required standard (trust me).
Oh, and did I mention WORK HARD when you get there...? Good luck from someone who's done the course...
