The Church was hugely powerful: Belief in heaven / hell, No education, so people learned from church, God punishes sinners, Disease is a punishment sent by God
Physician suggested a treatment for each symptom, including bleeding and purging; bathing (only available to rich); remedies (made from herbs and spices)
Practice basic hygiene (as recommended in the Regimen Sanitatis) and purifying bad air (eg carry a sweet-smelling "posy"; some measures were taken to keep towns clean, like clearing animal corpses) were prevention methods
The Church had less control over life, so there was a chance for the spread of new ideas. The printing press helped ideas to spread. The Royal Society allowed scientists to gather, share research
The Four Humours theory had been proved wrong by scientists. However, most people still believed it so most physicians continued to use old methods, eg bleeding