Crispy food needs enough oil to bind batters and coatings, but not too much or you'll end up with soggy results.

If the food has a crumbly or floury outside texture, try spraying it with a little bit more oil.   

If you're making air fried food from scratch, spray your homemade items with a light coating of oil (too much and the food won't get crispy) and arrange foods so the hot air circulates around each piece as much as possible.