While aluminum window frames are more function than beauty, you can keep them looking and working their best with a little periodic maintenance.
Consumer Reports, in How to Clean Practically Anything, recommends then polishing the runners with silicone car polish or oil to aid smooth window movements.
To keep up with fingerprints and fly specks, it may be best to use a window cleaner, and to do it before washing windows. Whatever you do, don’t use vinegar, particularly on those without a painted finish. It will chemically react with the aluminum, blackening cloth after cloth — as well as the aluminum — until you rinse with water and an absorbant cloth to remove the offending acid.