Describe approaches to registration.

Lock up the form.  Plan ahead so that the eventual placement of the paper guides will clear the tympan & frisket frames.  If you're using a Boxcar base, you'll want to be sure the guides aren't crushed into the base (or use some sort of low-profile guides).

Using a piece of carbon paper, print on the frisket.  Of course, ink will work too; the carbon paper just avoids a cleanup job.

Using a razor blade, cut a window (or perhaps several windows) in the frisket around the printed area.

Consider using plastic tape to reinforce and protect the edges of the frisket windows, especially if you aim to print on dampened paper. The clever person will put the tape on the frisket first; then cut away with razor.  I'll always seem to get it backwards.

Tape a large piece of scrap paper to the draw sheet (between the tympan and frisket), so that it covers the area to be printed.  The scrap paper should be larger than the desired product.

Using carbon paper, print on the scrap paper.  Leave the scrap paper taped in place.

Cut a piece of heavy mylar to match the size of the desired product.  Mark the mylar carefully to indicate the position of the text block.  Might add some extra horizontal and vertical lines to help achieve alignment.

Place the mylar on top of the scrap paper, being careful to align it perfectly.  Tape it in place on, say, the top and left side.

Now, without disturbing the placement of the mylar, trim away the bottom and right edges of the paper.  Trim enough so that the bottom and right edges of the mylar are exposed, but not so much that we can't double check the alignment of the mylar.

Place three guides along the bottom and right edges of the mylar.  Put two along the long edge and one on the short edge.  For larger pieces, more guides might be helpful.  Be very careful here, making sure that the mylar isn't forced out of position.

If you printing on paper with deckle edges all the way around, the problem is tougher; however, Phillip Gallo describes an approach in his blog that'll handle very irregular pieces of paper.  The essence of his scheme is to make a rectangular frisket-carrier sheet from two pieces of mylar.  The frisket-carrier sheet is used to hold the irregular paper and is itself placed on the tympan using ordinary guides.  Once again, I'll need pictures to illustrate his approach.

Imagine we're printing pages for a book.  If we print 2 pages on each side of a piece of paper, we'll eventually fold the paper in half and sew it into sections for binding.  Rummonds suggests using points to hold the paper in register, placing the points so they're aligned with the (eventual) fold in the paper, i.e., exactly in the center left to right.  Placement top to bottom should intercept the (eventual) needle holes, so that a sewn section has no extraneous holes at all and all the deckle edges are preserved.