I find it hard to palm mute standing up?

: Anyone got advice??

This might sound like a statement of teh obvious, but practice playing standing up. I always found all sorts of things more difficult standign up, and it put me off joining bands for ages. Then I realised that it's all bound to feel strange because the angles are different, so I started doing my practicing standing up. You'll soon get it. How exactly depends on what sort of bridge you've got and how high the strings are off the body. The technique would be quite different, for example, on a Telecaster to on a trem-equipped Strat. And my old Hofner's a whole other ball game! Have fun!