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Always turn OFF all power to the appliance before serving or making any kind of repair.
Do not attempt to replace ANY Electrical part if you do not feel comfortable working with electrical components. Working with fuses and breakers can sometimes expose you to lethal voltages. If in doubt, call for a license service company.
Never touch or move frayed wires if you are not sure that the power is turned off.
If you reset a breaker or replace fuse and it blows again as soon as you turn the power on, do not replace or turn it on again.
Do not install a bigger fuse! Call a license service company.
If you replace a fuse, always replace it with the correct amperage rating located on the equipment. Installing the wrong size fuse can create a fire hazard, or damage equipment.

Before working on any gas appliance turn the gas off.
If you are not familiar or comfortable working on any gas appliance call a license service company to make all repairs.
If you smell natural gas or propane, even if you don't have a gas line in your house or business -- report it to your natural gas supplier immediately. If the odor is strong, leave the house or office immediately and call your natural gas supplier from a neighbor's telephone.
Do not use your own telephone.
Never use matches to look for gas leaks and never try to look for the leak your-self. Don't flip a switch, since they can create sparks, and don't use any other electrical equipment. If the odor is strong, leave the house immediately.

Repeated pilot outages could indicate a hazardous condition. Don't attempt to re-light the pilot or service the equipment. Call a license service company.
If your appliance has been flooded, shut off the gas immediately. Do not use your gas system again until the wet or flooded equipment has been checked and serviced.
Do not store any type of combustibles near your furnace or heating equipment.
At the first indication of incomplete combustion (yellow flame instead of blue, or soot present), call a license service company immediately. Improper combustion can cause carbon monoxide buildup which good be potentially fatal!

Carbon Monoxide Poisoning: Although there may be no problem in your house, you should be alert to the causes of carbon monoxide poisoning. Common causes of carbon monoxide poisoning are malfunctioning heater vents or clogged chimneys. They should be checked occasionally to make sure they are free from obstructions. Your heater also releases water vapor that must get out through a vent or chimney. Otherwise, moisture in the chimney can cause gradual erosion of the chimney. If you have concerns, get expert advice from a qualified source.
Carbon monoxide poisoning symptoms can include dizziness, nausea, headache, weakness, and loss of muscle control, chest tightness, heart fluttering, sleepiness, redness of the skin, confusion, vomiting and diarrhea. Carbon monoxide poisoning should be suspected if more than one member of the family is sick and if they feel better after being away from home for a period of time.
People, who suspect they have been exposed to carbon monoxide, should immediately seek fresh air, if symptoms linger, they should see their doctor quickly.

You should be familiar with the manufactures specs on the particular appliance you are working on. You should also be familiar with all safety regulations listed on that particular appliance you are working on. Always follow the manufactures service, installation and safety warnings on the appliance.
If you are not sure on any of these procurers call a license service company.