Don't store your wax in the fridge or on a shelf attached to an external wall. Clean your burs. Make sure you select 'Wax' for your parameters so speeds are slower. Even if you have some undercuts, on a 4 axis mill you can position the undercuts along the Y axis. The puck holder can tilt a few degrees either way on the Y and get a good mill.
good info, i only want to say its not always a good idea to go slower. there is a relationship between how fast your spindle spins, and how quickly it moves point-to-point. this relationship is referred to by many CAM softwares as Cutting speed (as opposed to Spindle speed, or Table feed which are the factors of Cutting speed)
varying a single parameter of Cutting speed can be good, but also can be bad. in soft materials like zirconia and wax and plastic it is highly advantageous to use high cutting speed, especially if the machine can be kept vibration-free. in hard materials these kinds of high speed passes sometimes arent feasable.
for wax though, much as with plastic you want to push through the material quickly so that the spindle doesnt sit on any area long enough to create residual heat and melt the wax. too slow and you can have material "gum up" the tools.
for thin things though, no matter really what it is, veneers in wax, or thin zirconia, or thin titanium copings, avoiding chipping is the biggest objective, and the best guarantee of that is sharp clean NEW tools.