I found the following posted in our squad room.
THE TEN FATAL ERRORS THAT HAVE KILLED EXPERIENCED LAWMEN
1. Your Attitude - If you fail to keep your mind on the job while on patrol, or if you carry problems with you into the field, you will start to make errors. It can cost you or other fellow officers their lives.
2. Tombstone Courage - No one doubts that you are brave, but in any situation where time allows, wait for backup. You should not try to make a dangerous apprehension alone and unaided.
3. Not Enough Rest - To do your job, you must be alert. Being sleepy or asleep on the job is not only against regulations, but you endanger yourself, the community and all of your fellow officers.
4. Taking a Bad Position - Never let anyone you are questioning or about to stop get in a better position than you and your vehicle. There is no such thing as a routine call or stop.
5. Danger Signs - You will come to recognize "danger signs"--movements, strange cars, warnings that should alert you to watch your step and approach with caution. Know your beat, your community, and watch for anything that is out of place.
6. Failure To Watch The Hands Of a Suspect - Is he or she reaching for a weapon or getting ready to strike you? How else can a potential killer strike but with his or her hands?
7. Relaxing Too Soon - The "rut" of false alarms. Observe the activity, never take any call as routine or just another false alarm. It's your life on the line.
8. Improper Use or No Handcuffs - Once you have made an arrest, handcuff the prisoner properly.
9. No Search or Poor Search - There are so many places a suspect can hide weapons that your failure to search is a crime against fellow officers. Many criminals carry several weapons and are able and prepared to use them against you.
10. Dirty or Inoperative Weapon - Is your firearm clean? Will it fire? How about ammunition? When did you fire your weapon last so that you know if you can hit a target in combat conditions? What't the sense of carrying any firearm that may not work?
(The above was published by the National Association of Chiefs of Police.)
Most of this seems like common sense to me, but just like any other job, after you do it awhile, you get complacent. In most other jobs though, you're not likely to end up in the morgue.