Step 1: Safety
• Fry your turkey outside, away from anything flammable. As in, not on your wooden deck, inside your garage, in your kitchen, or anywhere that overflowing flaming oil would be catastrophic to your home. Read: concrete, dirt, gravel away from everything, on level ground. Put the propane tank as far away from the fryer as possible.
• Make sure your turkey is thawed and dry. A frozen turkey can explode, and a wet turkey will make the oil bubble to the point of overflowing when lowing in the turkey.
• Do not use too much oil. If the oil overflows, you've got potential for an oil fire. Most turkey fryers will have an oil line to save you the trouble, but when in doubt, put your turkey in the fryer, fill with water until turkey is covered, take out the turkey, and mark the water line so you know exactly how much oil to use.
• Don't leave the fryer unattended. Once the flame is on, keep an eye on the turkey and the temperature. If the oil starts smoking, turn down your heat. You want to cook at a steady 350 degrees.
• Lower turkey into the fryer slowly to avoid oil overflowing. You can turn off the burner during this process so if oil does spill it doesn't catch fire, then turn it back on once the turkey is in.
• Keep a fire extinguisher handy. Oil catches on fire if it exceeds a certain temperature. First it will smoke, so if you see the oil start to smoke turn down your heat. If there is a fire, it is an oil fire so do not use water to extinguish. If there is a fire, kill the flame and cover the pot if it's safe to do so, and if not call the fire department immediately.
Image courtesy of this site, which has further reading on safety guidelines.