There's actually a lot on bar care around the internet.
Depends on conditions.
And if you like the shiny or the oxidized look. My Axle is almost fully oxidized now, and I like that look. The old York bars I used to train on (30 years old) were fully oxidized.
I like to take a cloth and some WD40 and go over the parts I don't touch to help protect from moisture.
Do not store the bar loaded.