Sometimes it depends on the size/breed of chicken. But it is pretty universal to keep as close to 100 as possible. A little below or above is no big deal. Be sure to mark one side of the eggs with D for day and N for night and remember to turn.

If you have your average chicken egg incubator (Foam with wire tray) be sure to add a little of water in the bottom, but don't over-do this part.

A note to keep in mind, don't fret if your power goes off. Once while I was incubating Rhode Island Reds, the power went off for the best of two days, and I only had one out of thirty or so eggs not hatch.

Also, if you would like to check the fertility of your eggs, you can use a method called candling. Just cut a hole smaller than the egg size in a cardboard box, set the egg on the hole, and use a flashlight in the box to shine underneath the egg. In your textbook fertile egg you should see a nice red color with plenty of veins along the shell.

Hope this helped