1. Wash, peel (if you want), and cut your sweet potatoes into desired fry shape.
2. Boil a pot of water, and at the same time preheat oven to 400 degrees F. Drop the sweet potatoes in the boiling water for 5 minutes. Drain and pour out the potatoes onto a baking sheet.
3. Toss with salt, pepper, a bit of olive oil (I use olive oil spray to reduce the calories) and add any other spices you like. Once the potatoes are coated well enough lay them flat on the baking sheet.
4. Bake for about 15 minutes and then flip each fry carefully using tongs. Put back in oven for another 10 minutes or so until they are crispy on the outside and soft on the inside. The cooking time will vary depending on the size of your potato pieces.

I have found the most important trick is boiling them a bit first so they soften up. Some people do the same thing in the microwave, but I am not really a microwave fan.