If the bike is properly lubed it'll survive rain pretty well with no special help from you. How you do determines if you'll want fenders or not. I commute daily rain or shine, and do absolutely nothing after riding in the rain.
I used to bring the bike in immediately, but have recently made a small improvement. Now if when I get home the bike is mud splattered or covered in glued on leaves and twigs (I ride home through a park) I leave it outside a while in the rain which rinses it off fairly decently. I figure if Mother Nature got it dirty, it's her job to get it clean again.
This may sound neglectful, but isn't because the bike is kept waxed and lubed, and bare metal parts have a protective film that prevents rust. Water doesn't enter the bearings because it's repelled by the grease film. (no sealed bearings)
I don't think I could leave it outside long term without worry, but so far have never seen even the least hint of rust or mechanical failure. I also keep two bikes in Cozumel, Mexico where the air is both humid and full of sea salt. It's been 5 years and both of these are 99% rust free. (only some steel hardware here and there).
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