what rpm, depth of cut, feed are you using? vertical machining CNC?
the idea is to make the cutting edge take big bites into the plastic to make bigger chips than say cutting aluminum. this is relative depending on rpm and feed. so a suitable low rpm and high feed is a good start. Some spindles can only spin fast, which means your feed needs to be very high. High feeds can suffer accuracy issues for small features with sudden change of direction (like right angle motions become rounded) if motion acceleration cant match g-code without enough dwell time. An obvious tradeoff can be understood here. Sharp tools should be used that are dedicated for plastic (dont worry if you dont mess up the tools will likely last a very long time). Some say zero helix cutters are good. Ive seen some amazing plastic roughing cutters that can do depth of cut 2X the diameter of the tool and still come out ok.
Good old fashioned water maybe with some detergent in it (dish soap) under full flood cooling conditions is best. Often this may mean you cant use your flood coolant system if it was rigged to use some oil based coolant. For vertical machinig you can often just pour some water on a large flat stock if you are just cutting 2.5D stuff. Stuff held on a vice may require flood coolant with a nozzle and coolant flow.
Ensure good chip evacuation to prevent chip rubbing (!) and recutting that generates a lot of heat. Maybe play around with your depth of cut. Lower it for better results.