Business dress code:
In German business culture, particularly in old economy firms, dress is still fairly conservative. Dark suits, muted ties, and white and blue shirts are the norm. Blue blazers and grey flannel pants are also acceptable.

When you receive an invitation for a social gathering stating "informal" dress, this really means "smart casual", i.e. tastefully coordinated clothes, for example for men: no tie, polo shirt, jacket.

Gift Giving
There has recently been a move towards concentrating much more on the actual business and less on formalities and rituals like gift giving when travelling on business. However, for special occasions like retirements, weddings, or a visit to somebody's home, gift giving is customary and gifts will be appreciated. Especially when you have been invited to someone's home a small gift, such as flowers for the wife, a bottle of wine for the host or candy for the children will be expected and will be a sign of good manners and respect.