I rarely do everything "right". I have tendency to hatch shipped eggs, or mix breeds that need little humidity with higher humidity. I frequently begin Hatching in there middle of winter when the eggs may get chilled before I collect them.
That said, over the past five years, my hatch rate has varied from 0-90% on various hatched. 0 was winter shipped turkey eggs, 90 being fresh from my flock.
Overall, probably atound 60% on my own eggs. That is from eggs set, not eggs that make it to lockdown. There are always clears.
I don't assist. I did at one time, but found those I assisted tended toward weaker birds. Since I breed for survivability, I don't really want them in my flock.
I really don't obsess over humidity until lockdown. It is my personal opinion that while there is an " ideal" in nature there are great fluctuations. I know a lot of people mark air cells, weigh the eggs, etc. I have never done any of that. My time and schedule frequently does not allow me to check an incubator more than once a day, sometimes only once every three. This is why I normally run my incubators in my basement. There is almost always water seeping in around the edges, so there is some humidity.
Tomorrow I will set another group of eggs in the same incubator in my basement, not as any water until lockdown and see what happens. I will also put a recording thermometer in the incubator so I have an idea what the temperatures are.
I'm actually very satisfied with this hatch, even somewhat surprised.