Wood look metal door
I would just rub it with my hand first - then perhaps a very fine sandpaper - say 400 grit.
Make sure you are using a good quality Spar Varnish.
Why did the clear come off? Do you have a storm door to protect it? Is it at the bottom where it gets hit and kicked?
If you don't have a storm door for it - you might want to look into one.
As for it getting kicked - a nice brass kickplate would look really nice on a woodgrained door - and eliminate the wear issue at the bottom of the door.
Remember a house is never maintenance free.