[ASt85]

It is worth cleaning the car off with fresh water and allowing it to dry before storage. If you are keeping it under cover there is little to benefit from undersealing an already well protected car - the paintwork is a different matter.
It is worth applying a coat of hard wax like Simoniz or similar and leaving it unpolished, a friend swears by liquid paraffin - personally I think it is a little messy and difficult to remove later as it degrades - it also holds on to dust/diesel soot etc. if the paintwork is exposed - oddly applying a coating of diesel works well for vintage cellulose finishes.

If you are using a car cover, consider buying one of the more expensive breathable covers with a fleece lining - if it is straight waterproof pvc or similar you will get condensation build up between the cover and the paintwork.

Consider also using sponges to hold the cover clear of the larger panel paint work - I failed to do this when using a breathable cover over my son's '92 Eunos aka MX5 with the result that the very thin 2 coat of original paint bubbled on the bonnet where the cover was completely in contact with the bonnet. I now use long pieces of 5" x 5" sponge to keep the cover clear of the larger panels.

Disconnect the battery and consider using dehumidifier packs inside the car if the car is going to stand for a long period. Some salts left in the carpets from cleaning are deliquescent, traces of road salt are hygroscopic so the carpets will gradually become damp over time if the air isn't dry.

Definitely hand brake off, plus if it is a manual; you might want to think about keeping the clutch pedal depressed using a piece of wood or similar against the front seat to keep the clutch lining off the face of the flywheel as these too have a habit of freezing/sticking if left standing for lengthy periods. However there are those that would advise against keeping the clutch depressed as it puts a continuous load on the diaphragm/springs etc which may lead to distortion.

In any event a frozen clutch can quite often be cleared by bouncing the car back and forth in gear.