Wear bright, reflective outer layers. Wearing bright, reflective clothing is the one of the best things you can do, because then cars, bikes,and other runners can actually see you, especially if you're running in a wooded area. If you're wearing bright clothing, you're likely to be seen, which will keep you SAFE!
Bring identification and a cellphone. Both of these items will help if you find yourself in an emergency, lost or injured. I always try to let someone know where I'm going. Additionally, Iphone can be set up with a tracking, so your spouse can track your location if that feature is turned on.
Mace You can buy a keychain of mace and stick it in your pocket or clip it on to a hair tie on your wrist. The small mace costs $10, but can potentially save your life.
Running with a Partner: Running with a partner is always a great way to get a run done, especially a long run. It also is a great way to keep you safe. Run in numbers!
Run against traffic. Stick to sidewalks in well-lit areas when possible. If you must run on the road, which I do, make sure you face oncoming traffic so you can clearly see the cars. I know many people don't follow this thought process, but say to run with traffic, but I would rather see traffic coming at me.