What cultural faux pas should I try to avoid making in Hamburg?

"It is important to be aware of cultural differences when visiting Hamburg. It is important to be respectful of local customs and traditions, and to avoid making any offensive or inappropriate comments. It is also important to be aware of the local dress code and to dress appropriately for the occasion. Additionally, it is important to be aware of the local language and to avoid speaking English in public unless it is necessary. Finally, it is important to be aware of the local customs regarding tipping, as it is not customary to tip in Germany," said another expat in Hamburg, Germany.