Set the oven to 450 degrees Fahrenheit.
You can either peel the potato or leave the skin on - lately I leave it on every time. It adds nutrition and a nice chewy texture. :D
I don't worry about washing it, normally, but you can rinse it in the sink as long as you promise me you'll dry it off very, very well. If it's still wet the olive oil won't coat the fries as well, which will lead to soggy fries. And then you'll be disappointed with the fries and I'll be disappointed with you. :(
If your sweet potato has skinny ends, cut those off.