In the sauna wear your birthday suit or a towel. Nakedness is natural. There are no exact rules of behaviour but the ritual is meant to be relaxing. Hurry and noise are out of the question.
It is a good idea to begin with a wash or shower; a seat towel for the hot room is also useful.The temperature should be 80-90°C; ten minutes at a time will be enough.
Air humidity is regulated by ladling small doses of water onto the stove stones.
Warming up and cooling off can be repeated as many times as feels good.
Another brief warming-up may be nice after washing before finishing off with a shower.
Heavy meals and alcohol should be avoided before sauna. Afterwards you will need a refreshing drink and possibly a snack.
Sauna bathing in moderation suits everyone. Those with health problems should nevertheless consult a doctor before trying it.