Preheat air fryer to 400° Fahrenheit.
Once air fryer is preheated, lightly spray basket with neutral oil. Add frozen french fries to basket and lightly spray tops of fries with additional oil. Sprinkle salt or other seasoning over fries if desired, then place basket in air fryer.
Cook fries 5 minutes. After 5 minutes, remove basket from air fryer. Shake basket well to toss fries, and check doneness of fries. If desired doneness is not yet achieved, return basket to air fryer.
Cook fries another 5 minutes, then remove basket from air fryer. Check doneness of fries. If desired doneness is not yet achieved, shake basket again to toss fries. Return basket to air fryer and cook another 2 to 5 minutes.
Repeat steps 3 and 4 of cooking instructions as needed until desired doneness is achieved. Be sure to check doneness of fries and shake basket to toss fries every 3 to 5 minutes, or fries will overcook. See Notes below for suggested cook times.
Once desired doneness is achieved, remove basket from air fryer. Transfer prepared french fries to plate or bowl. Repeat entire process with any remaining fries until desired number of fries has been cooked. Serve fries hot with desired condiments and/or toppings.