When dealing with high voltages, corona discharges can easily form on sharp edges. For purpose of eliminating them, I made small guard rings by simply bending some papercilps.

Wires are to be soldered to center pins.

While this PCB is not particularly high-voltage (3kV), it's a piece of electron counter, so making it low noise was critical.

I use this technique on ion wind generators too, because corona discharges in undesired places make hissing noise, and may cause sparks.