Barring mecahnical adjuncts, another trick for one handed screw starts is to use a piece of electrical / duct tape on the end of your screwdriver to hold the screw in place until it seats.
Basically, you make a hole about the dia. of your screw shaft, slide it over the screw, sticky side towards the head, then seat the screw on the driver and press the tape onto the shaft.
Here's a bad ASCII illustration:
tape ------------------\
Screwdriver shaft +{========
tape ------------------/
The tape should provide enough hold to keep the screw a) seated and b) off the floor, and then by holding the tape and pulling away from the (now 3/4 inserted) screw, you can remove the tape and finish the screw placement.
+100 for the low-angle flashlight trick. Don;t forget to check under the nearest immovible object - usually about 2" farthe in then your longest reaching object