I feel that the best way to display a tapestry is by making a wooden frame, stretching the tapestry over the frame, and mounting the whole frame on the wall. This makes it easy to work all wrinkles out of the tapestry, and to make it into a square or rectangle even though the tapestry itself may be somewhat skewed from uneven shrinkage.
PLEASE NOTE: The following instructions are just my simple way of doing it. I know there are many woodworkers out there who could improve on them.
The size of the finished tapestries varies somewhat so the first step is to iron the tapestry, and measure it's dimensions allowing for a small amount of stretching. The frame dimensions should be a little smaller that the tapestry in both dimensions so that the tapestry can be folded over the edges and tacked. I used a staple gun to tack the edges of the tapestry. You could put a strip of wood over the edges to get a more finished look.
The frame can be made from one inch lumber that can be from 2" to 4" wide, or from strips of plywood. The corners can be square and butted together with an additional piece nailed on the back to join the corner, or the corners can be cut at 45 degree angles and a small triangular piece of plywood nailed on back to join them.