Three religious practices found in Mecca before Muhammad's revelations included the following:
Polytheism/Paganism: This was very widely practiced in Mecca before Muhammad began preaching. Polytheism in Mecca revolved around idolatry, with numerous idols being worshipped. Every tribe and house had their own idols, and the Kabah in Mecca was full of them. The Arabs at the time believed that the idols would bring them nearer to God and mediate with him for their sake. Though many idols were being worshipped, some idols of note include Hubal (placed in the middle of the Kabah), Manat (near the Red Sea), and Al-Lat (in the city of Taif near Mecca). During the conquest of Mecca later after the revelations of Muhammad, 360 idols were found around the Kabah; they were then removed and burned up.
Judaism: Jews migrated to Arabia in two major phases, once in 587 BC when the Jews left Palestine, and then again in 70 AD with the Roman occupation of Palestine. There were organized into various tribes and villages during the time of Muhammad. Some of the famous Jewish tribes included the Khabeer, Quraizah, and Qainuqa.
Christianity: Christianity entered Arabia via the Ethiopian and Roman colonists in the area. The Ethiopians managed to enter Yemen and even built a church with the aim of redirecting pilgrims from Mecca toward Yemen, but they were unsuccessful in their attempt. Followers of Christianity and Judaism were minor compared to the following of Arab Paganism.
Muhammad would later, at the age of 40, receive the revelation detailing the teachings of Islam. These teachings would change the face of Mecca forever.