I have never calibrated my hygrometer so I have no idea what he actual humidity is in the incubator, just what it is reading. Through trial and error I've learned that I get better hatches when the average humidity is around 39 to 40% on this hygrometer. I always go above a 65% reading on this hygrometer during lockdown.
I use a Genesis Hovabator 1588, one of those Styrofoam incubators with reservoirs in the bottom for water. Depending on the time of the year I can get some pretty wild differences in that humidity reading even with the same reservoir filled, maybe a 20% swing. It's not always possible for me to get exactly a 39% humidity reading. I go by average humidity during incubation. If it runs ate 50% for three or four days I'll try to run it an equal amount of time at 30% (or close) to balance it out. It's the average over the incubation that counts, not an instantaneous humidity.
Mine is a forced air so I can take the temperature any where in there. I put my incubator where it is not in direct sunlight, not where it is hit by air from a vent, and not where opening a door can cause a big change in temperature or the humidity of the air going into the incubator. In other words, a stable environment. Put it where pets cannot cause problems.
My tips. Read the instructions that come with your incubator and pay more attention to them than anything I or anyone else on here says, especially for your first time. You need to get to know your incubator, even similar makes and models can require different tweaks. There can be some trial and error in learning what works best for you. Different incubators can have different ways of positioning the eggs or different types of turners if you get an automatic turner. Learn the specific way your incubator works, it can be quite a bit different from mine.
When you get it, plug it in where you are going to hatch and play with it a few days. See what effects you have if you change something, especially humidity. If it is like mine with the different reservoirs try filling different ones and give it a chance to stabilizer, see what effects different reservoirs have.
Start all the eggs at the same time. Stay far away from those staggered hatches, at least until you gain experience. A staggered hatch is going to increase your stress levels and increase your chances for serious problems.
Calibrate your thermometer. The factory settings and the thermometers that come with any of them can be off. Never trust any thermometer that has not been calibrated.
Don't panic if someone on here tells you that your incubator will not work. The top of the line incubators are generally easier to use but a lot of chicks have been hatched in those cheap Styrofoam still air incubators. You may have to work harder or pay more attention to details but they can work well.
Mother Nature was very kind to us. A lot of research has shown what the ideal conditions are to get a good hatch, and a few of those are pretty critical. For instance incubating the eggs pointy side down (if you stand them up, many people don't) is pretty important in keeping the air cell in the fat end where it needs to be. But the temperature or humidity can be off a little and you can still get a great hatch. Mother Nature did not make it that hard for a broody hen to hatch eggs. Get as close as you reasonably can to the ideals, but there are windows that work. Temperature is more important than humidity but even if you are off a half degree in temperature you will still probably get a good hatch. It just might be early or late.
Don't panic if something goes wrong. Don't do anything dramatic until you've calmed down and chatted with us about it. Temperature spikes happen. Power goes out. Candling may not always go as you expect. These things are not good but they are not immediate death sentences either. Many chicks have hatched even if the power was off for a long time.
Don't expect your first hatch to go perfectly. Once the eggs go in the incubator they become precious, I understand that. A lot of people do get good hatches their first time. But sometimes there is a bit of trial and error and there can be a learning curve.
