On-Press Registration Card
There are lots of "tricks of the trade" to dialing in registration once you get to the press, but I've found nothing that works better than this On-Press Registration Card. It's printed on high-quality styrene material (like plastic) so you can lay it on your sticky platens with no worries of it tearing when you pull it up. Stick this thing down on a platen then line up all your screens to it and you're good to go.