I don't own a G20, but I own a car. Since you have a new car, I would just be gentle during the break-in period and don't do crazy things. Don't drive hard, or speed like crazy etc. Let the engine settle good and you should be fine. As for the interior, you want to stay away from chemicals that with time, will eat it i.e. Amor all, turtle wax, etc. Just make sure that every now and then you clean the interior with some form of leather treatment. If you have carpets inside, once a year get them shampooed. Exterior wise, you should wax it once a year or depending on where you live, twice a year.
Aggressive driving will definitely not be good so just take it easy on her during her virgin years. After a while, you might want to mod, then come back and ask what mods to do. Unless you want to start now, then we'll address it.
