My southwestern spiced sweet potatoe fries weren't crispy. What did I do wrong? What's the trick when you bake them?

If your fries are layered on top of eachother it will reduce the direct heat each fry is getting. To make crispy fries, make sure you tossed your potatoes in a fat then spread them evenly over your baking sheet. Halfway through the cooking process open the oven and shake the pan to rotate the potatoes and ensure even cooking on all sides. Again, keep your oven hot. 425+

Thanks! I used a 425 degree oven as the recipe stated. Is it crucial that the fries are spread on a single layer?

Get that oven HOT and make sure there is fat (i.e. oil) on the fries, but not too much. I like to make oven fries in at least a 400 degree Fahrenheit oven, sometimes 450 degrees Fahrenheit. You can also bake them at a much lower temperature and blast them for a few minutes towards the end. That would be much easier (and saner).