Suspend your mirror ball where you want it to hang, making sure it is firmly attached, and poses no danger to anyone below it.
Select two matching lights for your mirror ball. If you have access to theatrical lighting instrument, ellipsoidal reflector spot units with adjustable irises offer the most control. Small, tightly focused lighting units known as pin spots are also common for mirror ball lighting. For small at-home installations, clip-style reading lights with adjustable necks may work.
Position one light on each side of the mirror ball, slightly below the midline (widest portion) on a sphere or the rim on a half-sphere--about 15 degrees below the ball is a good angle for most situations. Aim the light at the mirror ball and either adjust its features so it lights only the mirror ball and not the surrounding areas, or adjust the lights' distance from the mirror ball to produce the same effect.
Clamp or otherwise affix your lights in place once they are focused on the ball. If placed correctly, each one will light exactly one half of the sphere, reflecting light to all sides and below the mirror ball. For half-sphere mirror balls, you may need to position your lights lower to avoid excess light spilling over the top of the bulb.