Hi,
I have had good results using two lines- one marking the center of the dado or whatever you are routing, and one parallel to the edge you are routing along (as well as the center line) placed about 2" or so from the center line.
Place the guide rail anti-splinter strip edge along the parallel line. Put the router on, then just fine tune the router onto the center line using the marks on the base. Make sure you are looking straight down when you align the router over the mark.
This works well and is quite fast to layout.
You can also place start and stop marks for stopped routes, and use the center marks on the sides of the router base. When doing this just remember to add or subtract the radius of the bit to the stopped route length.
Seth