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It certainly helps to have the hand anchored. I’m used to use my pinkie finger on the pick guard and will still use it for tricky songs that require a lot of precision string skipping. My in-person teacher has been teaching me to use my curled fingers and have them resting directly on the strings that I am not playing. I pivot the hand up and down depending on whether I am playing the upper strings or the lower strings.
As for improving accuracy I practice picking every single day. I have routines doing all down picks, all up picks, inside picking (up on top string, down on lower string), outside picking (down on top string, up on lower strings), string skipping, etc. I initially started at 60 bpm and am now up at 120 bpm for most exercises, It is a difficult skill to get good at.