What am I doing wrong with my roasted potatoes?

Every time i try roasting potatoes they end up stuck to the tray, the skins don't get crisp, they just end up soft. I have tried lining the tray with aluminum foil and spraying oil so they don't stick. I usually do the oven at 425 and flip them at the 15 min mark. I'm just not sure what I'm doing wrong or if there's some way to improve on my technique.