When eggs arrive, they should be removed from packaging and placed pointed end down in a cool place to settle for 24 hours, then brought up to room temperature before setting under a broody or in the incubator.
Before incubating the eggs you should ensure that your incubator has been running for 24 hours at a consistant temperature. I set my incubator to 37.5c. Check with a different thermometer to check the calibration of your incubator. If the temperatures varies between them, you should contact the manufacturer.
By allowing the temperature to stabalise you can make any adjustments before the eggs are introduced. Make sure you record the date you put the eggs in!!

Place the eggs in the incubator and then leave them! Only open to check water levels or to turn the eggs if necessary. When the eggs reach the seven day point they can be candled to check whether they are fertile or not. Candling is the process of seeing inside of an egg with a bright light to determine if the how the egg is progressing.

For manual incubators turn the eggs a minimum of 4 times a day. When the eggs are placed in the incubator an X should be placed on one side of each egg to keep track of the turning process. Use a pencil to lightly draw the X on the egg shell. Do not turn the eggs three days before hatching and check the incubator instructions for details of any adjustments required (useally an increase in water to increase the humidity for hatching). The hatching time varies from species to species --- chickens take about 21 days while ducks take about 37 days. Check a reliable source to see how long the species of poultry you are hatching takes to hatch as some bantam breeds can take as little as 18 days.