Two tabs on the longest side, and the closest corner, so it's easy to reach. Put your corner tabs close together so you can feel them/hold the paper against them with 1 finger, the slide the paper into the side tab.
with deckle, if you don't want to trim it off, trim your corner with scissors, make a small cut about 1/4-1/2" long - just long enough for the register tab (make it small), and then another at the other end of the long side, just take the deckleing off so you have a solid edge. You won't notice visually.
But - this is important - you have to use the same setup piece for each colour to get the location/angle exact for the register tab. mark it on the paper. If this changes slightly you are screwed.