Apply plumber's grease to the faucet's O-rings and slide them back over the base of the faucet so each one rests in one of the two channels. Slide the spout back over the faucet's base, wiggling it left and right until it sits firmly in place.
Insert the O-rings in the faucet's plastic valve disc, if the faucet is so equipped, and then insert the valve disc into the hole in the top of the faucet. Coat the faucet's valve parts with plumber's grease.
Twist the faucet's plastic valve cartridge clockwise, if the faucet has a cartridge, using a wrench to turn it until you feel resistance. Place the new rubber seats and metal springs in their slots inside the faucet, using a pair of tweezers. Next, press the ball assembly into the faucet and slide the plastic packing and cam back over the ball.
Insert and tighten any screws in empty screw holes in the faucet assembly, and reinsert any metal pins or clips into their slots. Turn the metal dome piece or plastic retainer nut that sits over the faucet assembly clockwise, using a pair of pliers whose jaws are wrapped with electrical tape to tighten the cap completely.
Insert any plastic adapter pieces in place and tighten the adapter's retaining screw, using a screwdriver. Place the faucet's handle on the top of the faucet and tighten the handle's retaining screw, using an Allen wrench.
Turn on the water supply to the faucet by either turning the handles under the sink counterclockwise or by opening the house's main water valve. Turn on the faucet and inspect it for any leaks.