I recently replaced my screw type sockets with fluorescent ballasts. I went with 4ft, single bulb, T5, 28 watt (standard output) ballasts because they were the most efficient and relatively cheap. You may want to go with the T8 size since that is more common, although efficiency is slightly lower.
First, paint your garage white as others have suggested. This is a must.
Next, determine where your studs are, and which direction they run.
Then mount a 4ft fluorescent light to the studs as close to the existing bulbs as possible, and use the same wiring to power the fixtures.
You have 4 existing lights, so you will mount 4 new florescent fixtures. I think single bulb fixtures will output enough light if you paint the garage white, but if you want even more light, go with 8ft double-length fixtures.
Summary of bulb efficiency
Also get a
reel light with receptacle and mount it to the ceiling near the center of the garage so you can easily drag light and power wherever it's needed.