Practice, practice, practice.
That's my best advice really.
I've just go my results from M1 (AQA) and will be doing M2 as part of further maths next year. To be honest I'm kind of dreading it because I struggled to get to grips with Mechanics at first (and I'm the only one in my further maths class who hasn't taken physics) but I kept going through past papers and revising modules with the help of one of my teachers and managed to come out with an A in the exam this year!
Just keep trying and soon enough it will click, then you'll wonder how you ever found it difficult.