While you may not be running enough for this to come into play, you should take a look at the shoes you're running in. Different bio-mechanics affect how you run, and where the stress from hitting the pavement goes. Foot Locker will analyze your foot type for free.

I also had very weak ankles, which meant lots of sprains. You can strengthen them by doing some easy exercises.

Try sitting on the counter with a bucket hanging on your toes (with shoes, or it will dig in). You can put stuff in the bucket to increase the weight. Then lift and lower the bucket by flexing your feet at your ankles. Don't use liquid in the bucket, for obvious reasons...

The other is to push your foot against some resistance. Try sitting on the floor with your leg straight in front of you. Holding the ends of a towel, loop the towel around the ball of your foot. Then push against the towel- you determine the resistance by how tightly you hold the towel.

I don't think I explained those very well. Sorry.

Hope it helps! BTW, I've been running for years now- with happy ankles.