Here's how I love to season my sweet potato fries.
Placed the uncooked sweet potato fries into a mixing bowl or a plastic bag, or just onto your baking sheet and then sprinkle the sweet potato fries with cornstarch and pour in a few tablespoons of olive oil, enough to lightly coat the fries.
Then season the sweet potato fries with salt and pepper.
Garlic Powder and Chili Powder are also good to season sweet potato fries.