1 Stopping worrying about kit. Some cameras are better than others for some applications, but the main thing is to use equipment you're happy with and can use quickly and comfortably, almost instinctively. For LF, unless you use it very often, consider checklists.
2 Stopping worrying about pointless pseudo-refinements such as the Zone System. It's basic sensitometry, wordily restated. If you want to know what you're doing, read a real book about it. You'll generally find that it doesn't matter all that much anyway. Much the same applies to real refinements such as MTF curves.
3 Remembering that if you don't play, you can't win. So play as much as you can!
Cheers,
R.