When/how to prepare for STEP/TMUA?

I'm currently a Year 12 student halfway through my second term at school studying double maths, physics and economics. I intend on doing some maths related degree at university - (e.g. maths, maths+compsci, maths + philosophy, applied maths etc.), however am not locked in on one yet.

I want to do this at oxbridge, which will require me to do the TMUA at the very least and maybe STEP if I want to go to cambridge - currently my maths isn't brilliant, I scraped entry to BMO1 this year.

I was wondering how should I best prepare for these two exams over the course of the next 10 months for the TMUA and year and a half for STEP?

MEI has some prep courses
https://www.physicsandmathstutor.com/admissions/step/ - look at the "advanced problems in core mathematics" book here
For TMUA: https://old.reddit.com/r/6thForm/comments/1luzdm3/how_to_succeed_in_the_tmua_from_a_90_student/

Thanks so much for this - for your TMUA link (the roadmap) - given that Im only 10 months away from the TMUA, will I have time to complete it fully? Or am I overestimating how much of a workload that is (given I'll have to balance it with school and other stuff too).

I'm currently a Year 12 student halfway through my second term at school studying double maths, physics and economics. I intend on doing some maths related degree at university - (e.g. maths, maths+compsci, maths + philosophy, applied maths etc.), however am not locked in on one yet.
I want to do this at oxbridge, which will require me to do the TMUA at the very least and maybe STEP if I want to go to cambridge - currently my maths isn't brilliant, I scraped entry to BMO1 this year.
I was wondering how should I best prepare for these two exams over the course of the next 10 months for the TMUA and year and a half for STEP?