OSHA has a pretty comprehensive fall prevention campaign going. They've got big picture guidelines for overall safety at heights. I'd like to share a few simple thoughts on what you can do personally to stay safe while working up high.
1. Always use the correct gear - don't settle for the wrong sized harness or improper material for a lifeline, get the right stuff and use it. 2. Get trained on the proper way to install and use your safety gear - great equipment that isn't used correctly can be worse than no gear at all. 3. Clear the area you're working in of loose debris and unnecessary materials and keep an eye out during your work day for stuff that gets dropped or left lying around even after you've cleaned up. Eliminate extra equipment you don't need. 4. Avoid working at heights when you're super stressed or extremely tired, you need your wits about you when you're in a potential fall area. 5. Be aware of anything you ingest (like prescriptions or cold medicine) that could alter your balance and or depth perception - two things you need to stay upright and safe.
Keep these things in mind and you'll keep yourself out of OSHA's statistics.