The secret to awesome oven fries is presoaking them in salted water, which makes the potatoes release a bunch of their moisture before cooking. This ensures they will crisp up without having to risk burning them.
Sweet Potato Fries - soak cut sweet potatoes in water for at least 1 hour up to half a day. Remove from water and shake dry then lightly coat with cornstarch by shaking in a ziploc bag. Then proceed to season and oil as recipe indicates.