I use the cheap v-bits for milling the perimeter (cutting out the board).
I use 0.5 mm end mills for the isolation pass with a depth of 3 mils (~0.08 mm). The only way this works is using the Autoleveler program Gaston mentioned. I don't take any special care to level the board. My CNC bed is fly cut but I use a piece of scrap wood on top of the bed and attach the PCB blank to the board with double sided carpet tape. I typically set the Autoleveler to probe the board about every 1/2 inch (~12mm). Flooding the board with a thin layer of cutting oil after probing and before cutting gives much cleaner traces. The oil also keeps the dust down. I use a 0.8 mm drill for all holes and hand drill or ream larger holes after machining is complete.
I only make single sided boards and seldom design traces less than 20 mils (~0.5mm).
I like following this group as I'm always ready to learn better ways.