My best advice is, whenever possible, pull the skin and or move your head so you are shaving on a flat or convex surface. If convex, be especially careful with the amount of force you use (razor to skin), as the surface area is even smaller than normal, which means more pressure per amount of force (i.e. if you use the same force you always use, you'll get more pressure than you'd normally have). If you have to shave a concave area, try to find a curved part of the blade that has the same or smaller curvature than the concave area.

Whenever shaving a non-flat (concave or convex) area, remember that you cannot judge the angle of the blade with respect to the parts of your face that you can see, because the part of your face you see is not at the same angle as the part of your face you are shaving. (I aim for what looks like a much shallower angle to err on the side of caution.)