1) Turn off your cell phone. Sometimes, your cell phone may ring or make a noise, which would disturb the other people within the masjid, whether they are praying, reading the Quran, or just talking about the Deen.
2) Put your shoes in the shoe rack. Leaving them on the floor may present a hazard for people who may accidentally trip on your shoes.
3) Keep your children under control. If your children are not under control, they can distract other people within the masjid.
4) Please ask for permission from the administration of the masjid before posting anything. Different masjids have different rules on the display of advertisements and flyers, and it is good to get approval for your activities first.
5) Please keep the house of Allah clean, both inside and outside. Cleanliness is a good thing. Avoid placing shoes, food or drink inside the prayer area.
May Allah make it easy for us to follow these 5 Etquettes. Jazakallah Khair.
Source: “Etiquettes of Masjid”, a poster in Masjid Ul’ Aala