All depends a bit on how long you want to store it.
Remove battery and keep it in your flat, charge once a month (or keep on trickle charger).
Pump up pressure in tyres to 3.5 bars (or 3 bars if that is maximum that is all that is allowable on your tyres), alternatively put on stands but allow wheels to keep in contact with ground.
If garage is dry leave windows about an inch open, if not then keep closed and put in a dryer (one of the small room dehumidifiers with 'tablet' in).
If last oil change was a while ago change the oil after getting engine up to full temp (drive 50 miles). Then change oil, drive for it to get to temp again (to make sure exhaust is free of condensate). If coolant is very old change it too. If it has aircon check coolant level before and after parking up if its performance is not good.
Obviously clean inside and out.....
Lastly place cardboard under the car (to see if it leaks anywhere).
Leave with reasonable amount of petrol but not a full tank.
