Any exposed metal will be prone to oxidisation, especially if the people in charge of roads salt them in winter. ACF50 after a good wash should help protect it. Other products from wd40 and scottoiler are available but ACF50 seems to get the best reviews.
Rinse the bike down after a wet ride or after riding on freshly salted roads.
If your bike has a plastic tank drain it before laying it up, if its steel, it may be better to fill it right up to inhibit rusting.
I would also put it up on front and rear paddock stands to stop the tyres deforming and then hook up a battery tender to keep the battery in good shape.
Finally i take the opportunity each winter to do an oil and brake/clutch fluid change.