Achilles Tendinitis - The no fun injury, happens to runners like me sometimes.
I developed this injury in March 2006, and it is a nagging injury. It can take a long time to get over, this is a serious injury.
How do you avoid achilles tendonitis to start with? Well, make sure you have good running shoes, and that you don't increase your mileage suddenly - that will increase the stress on not just the achilles tendon, but the rest of your body too. It can lead to other injuries as well.
You have to rest for quite a long time. Don't even think about easy running. If you start running too soon before the tendon has repaired itself, you get the same injury back again and your running will be put on hold even longer.
Take it easy when you start running again. Avoid hills and uneven footing. Go shorter distances and avoid fast running for a while. It's important that you build up your mileage carefully and gradually, otherwise it is very likely that your achilles tendon will flare up again.
Icing the injured area may help, so definitely try it. I think enough rest is the best solution off the bat though. Good luck!
When you start running again, avoid uneven surfaces. Stick to flat surfaces as much as possible, and avoid any kind of hill running, up or down.