Commute Orlando has produced some good materials about bicycling best practices, including the excellent video below.
Lane positioning demonstration video
When a travel lane is too narrow, bicyclists are encouraged to "take the lane." But how should this be done? The League of American Bicyclists has long recommended that bicyclists position themselves about where the right wheels of vehicles go. This short video shows what happens when a bicyclist rides in the middle of the lane (from the beginning to the 2:12 minute mark) and in the right wheel track (the remainder of the video). Not only is the middle of the lane safer (with far fewer close passes), it also causes less disruption to motorists because they change lanes sooner.
This is a road with more than one lane going in the same direction, and it is not clear whether it would generalize to two-lane roads. My personal experience on two-lane roads is that riding close to the white line on the right results in a lot of close passes, riding in the right wheel track gets significantly fewer close passes, and riding in the middle lane gets even fewer.
Lane Control v Right Tire Track Video
For a more detailed description of what is happening in the video, see: Helping motorists with lane positioning.