As far as the body goes...
Rear edges of the sills go, inside and outside
Rear edge of floor, seam rusts then flakes off
Front floor where it meets the bottom of the bulkhead
Inside the rear arches, rust holes inside the front edge is an MOT fail because its close to the seatbelt mounting, rust at the rear of the arch isnt as much a problem
Below the mirrors
Along the inside bottom edge of the doors
Along the bottom of the rear windows
Mechanically...
Exhaust bracket in front of the 2nd cat usually dissolves
On the rear axle (either side around the spring base, saw a few like that now)
Battery tray
Fuel tank straps