Find the rust early. remove the paint at least 1/4 inch around the rusted areas. Buy a POR15 starter kit for about 30$ and follow the instructions exactly. In places along seams, after the POR has dried for a day or two put Black flexible seam sealer. I use a bondo spreader cut down small enough to spread in the area I'm filling.
After one winter I had only one small spot that I forgot to seal properly come back with a tiny speck of rust. I have now cleaned and re-sealed it and I'm 100% it's good to go!
I'd start looking around the back sides of panels, bottom inside seams of the doors, inside edges of the trunk, and under the car along places which could have been scraped or had the rustproofing blasted off by winter salt/sand.
Performance one step at a time.