I have always had to keep my bikes outside (no space and living in flats etc), here are my pointers.
Cover cover cover. Not only does it shield your bike from dust and keep it dry, it also keeps it out of mind of potential criminals. A cover also means that people won't just decide to sit on your bike if they are drunk (again depends on where you live, but this has happened to my bike). People won't know whether its a shit or good bike because it's covered
Make sure you get a good chain for the rear tyre - hopefully you can chain the bike to a pole or something, AND a disc lock for the front wheel. With reminder strap of course

! Again because the bike is outside you want it to remain as inconspicuous as possible, with as much security. A nice bonus of a cover is that you can put the chain on the inside of the cover or out, up to you.
As far as cleaning goes, my experience is that wiping down the disc brakes helps loads with rust during the winter, as well as just giving it a hand wash with water. You will need to lube your chain more often with the bike outside.
As for keeping it spotless, good luck! My philosophy was always to spend my time riding bikes rather than cleaning them, so I don't a dirty bike, but that said it's always nice to have her shiny again.