Assuming you're running the correct talents and everything, there isn't much to miss really other than practice. Spend an hour or two (yes legit an hour or two) practicing on a training dummy. Opener if you're running horn of winter should be RW -> Oblit 2x (press rime if it procs) -> pillar/breath/racial/trinket/abom limb macro. Then oblit one or two times once breath is ticking to drain runes and press horn to get it on cooldown. Then just oblit when you're not runic power (I don't press it above ~105ish, which isn't very often anyway), and press rime when it procs. You're going to press ERW 30-45 seconds in, takes some feel to get used to when to use it optimally, but there's some rng in there as well due to hysteria procs. As a rule of thumb press it when you're at like 75ish RP and have 1 or 0 runes. You can't press it when you're completely starved or it's not going to save you.

I will say one frustration I've been having so far is that some breaths just get absolutely fucked by not getting procs, feels really awful when that happens. Meanwhile other pulls I've had breaths last so long I had to press frost strike to kill them because it was back up again and I didn't want to fuck up cooldown timings with my trinket.