Hi Anthony,

First up, make sure you declare the car as off the road from the start with Revenue, as you cannot do that afterwards. It can be done online here.

Aside from that, give the car a thorough clean inside and out, and underneath if possible, then make sure it's completely dry.

Ensure the parking brake is disabled so it can't stick on.

Ideally you'd have the car up on stands and the wheels off and stored to prevent damage to the tyres. Cover the brakes up if you do that to reduce the chances of rust. 

Parking on grass for a long time is not ideal, as it's likely growth and wildlife will get into the car from underneath. If possible park on a hard surface where there is no growth, or consider putting plastic sheeting under the car. 

Finally, cover the car as completely as you can, as sealed from air and water ingress as possible. 

Using a trickle charger to keep the battery in good working order would be no harm either.