I'm assuming your using VersWorks as your RIP?
In the clip and tile menu you'll find the Tiling section. We normally stick to manual tiling and drag the blue bar that's in the middle of the print up or down depending on if you want one section to use up more print space than another, or if you want them to be evened out. The blue bar should stop moving once one section reaches the Media Width.
In the Overlap section we've been using the Top-Left type of overprint. As for the size of the overprint maybe an inch or so? Others may have to help me out on this because I'm trying to remember if VersaWorks overprint would be an inch on either side or an inch cumulative.
You'll see the overprint area represented as dotted lines above and bellow the blue line. They'll change position as you increase or decrease the overprint size so you'll be able to see where the overprint will be to maximize overlapping points for a straight print.
Right clicking the selection will make is disappear and not print that section. Right clicking it again will make it reappear. I know you didn't ask for that, but I thought I'd throw it in since it confuses me every...time.
Usually whenever we have printed overprints it has not been with overlap lines, but also these prints have have plenty of letters and graphics overlapping that we are able to use those as line up points. So that choice is up to you so long as the print is not crooked.
Hope this helps some.