Roof along gutters, inside under headlining
bottom corners of boot lid back edge
bottom corners of all four doors on the outside
bottom inner corners and top inner corners of the front doors
all around the front and rear windscreens
bottom front corners of the rear lower quarter panels
top of the dogleg panels
bottom of the dogleg panels
sill panels
bottom of the front guards
front corners of the bonnet
floors

Anywhere that shows any sign of surface rust on the outside has about fifty times more rust on the inside.

Look up under the dash at the bottom of the plenumn. They can rust out from underneath and not be visible from outside under the windscreen.

Have a look at Rare Spares rust panels. That will give you an idea of the main areas that rust. Of course there a lot of other places that rust as well. Good luck with the job.