Top tip: it's all about muscle memory!
Can you remember exactly how you felt when you achieved your best? I expect you felt really elated, but what do you recall about how you felt physically?
Chances are, your postural support was organised for maximum efficiency - and you need to access those memories to create the habits which reproduce success.
I show people how to do this in great detail but you can have a go yourself - like Jonny Wilkinson preparing to score!
Prior to riding, or playing golf, or music, or going on stage, try spending a few minutes going through it all in your mind - if you can breathe slowly, or even better, lie down, this could be reeeeally useful.