What are the etiquettes of visiting a mosque?

Mosques are sacred places. Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (peace be upon him) said: عَنْ أَبِي هُرَيْرَةَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ...