I have tried the dry incubation that some people recommend for Marans eggs and I dont really care for it. The chicks seem to hatch much better when I aim to keep humidity around 35-40% for the first 18 days and up to 65-70% at lockdown. I've hatched Marans alongside our other breeds with humidity in the 40's the first 18 days and have done well. Humidity is important, but what is more important is temp and ventilation. Keep a small hole open and your temp on point. Try to avoid temp spikes if you have a manual thermostat. Temp a tad low wont harm the eggs, but it will increase gestation length (chicks hatch later). But a temp spike too high can nuke the whole batch.
Regulate your temp for a day or so prior to setting eggs to make sure it is good. When you add eggs you may notice the temp is lower for a bit but dont regulate the thermostat. Unheated eggs can cause it to be low until they warm to set temp. Wait 24 hours before increasing temp because it will usually come up.
Unplug or turn off the incubator when you open it.
That's all I can think of for now.
Congratulations on your new incubator! Post lots of pics of your babies when they hatch!