Most red marks on the face are caused by over tightening the CPAP mask. CPAP masks should only be tightened down enough to create a seal. To avoid over tightening your mask, you should work clockwise around the mask, making small adjustments to the headgear, until the mask is securely in place but not overly tight. You should avoid pulling too much on one side of the mask than then other.
By cleaning your mask cushion, nasal pillows, and nasal prongs on a daily basis, you ensure a better seal each time you put on your mask. If you know you have a mask that fits, and are cleaning it daily, and still have red marks, consider using mask strap pads which are soft covering for the headgear straps.