Read the sticky note on hatching and incubating eggs:
https://www.backyardchickens.com/forum/viewtopic.php?id=48726.
Then do a search for topics like: humidity, temp, lockdown, etc.
I found BYC to be great help. Listen to the folks with experience!
I'm a newbie, just now going through my second hatch and having great luck so far! My first hatch was ruined because I opened the incubator on the last day and lost a lot of humidity--I actually drove the incubator unplugged for 30 miles to transport it to my house from my kids' school. Bad mistake....
Make sure you run your incubator for a good day or so before putting the eggs in. This means you need to plan for the arrival of the eggs. It took my
Brinsea 20 about a day for me to get the temp and humidity just right. The factory settings were no where near 99.5 deg. Then I put in the eggs and watched, watched, watched to make sure temp and humidity stayed good (had to adjust a little bit more).
Same with the styrofoam incubators, had to take 2 days to stabilize one of them, 3 for the other! but it is an LG and is trouble all around. I had several eggs quit on me in that incubator, but very few in my other one, my HovaBator.
I'm using the
Brinsea for hatching this time, will incubate in it later after this hatch is over and I've gotten over the glow!
Read the instructions you got with the incubator, then get more info here and on other sites such as feathersite.com and My Pet Chicken.
Generally, if you have a fan, the temp should be 99.5-100 deg F, humidity can be as low as 30% if you dry incubate (my best hatch was dry this time) or 45% for the "normal" way. Humidity needs to go up (i.e. add water to the channels) on the 18th day, some say to 65-70% or more (until the window of the incubator is fogged up according to some), others say 55% is fine. I am keeping mine at 65-70% and things look good.
Again, read and read whatever you can well before you start. Don't make the mistakes I made by being ignorant. Dead chicks are a huge drag.
Have fun!