Be sure you have your temperature settings at appropriate levels by conducting as many test runs as needed with water in the pan of your incubator. When you first place the eggs in your incubator, do not make temperature adjustments until the system has had adequate time to stabilize. Upwards adjustments too soon can cook your eggs and end your hatch. Humidity -tends to be overlooked and problems with humidity can cause major hatching problems. Test the humidity within your incubator using a hygrometer, or you can calculate the relative humidity using the wet bulb technique.
Hygrometers are simple and relatively inexpensive.
Your specific incubator will have recommended humidity levels. Ventilation -hatching eggs need fresh air to avoid suffocation. Styrofoam incubators have holes for ventilation that have to be open. Be sure you haven't obstructed any of these vents by the placement of your incubator. Holes can also become plugged between hatches while cleaning your incubator be sure to inspect the vents for patency.