Lacing embroidery in preparation for framing is quite easy. All you need is:
Lightweight wadding or felt
Strong thread such as perle 8 for lacing.
For the card, I use a 2mm (1/16") foamcore. It is not too thick but firm enough to support the embroidery.
For padding you can use wadding, felt or even wool flannel. Putting padding behind the fabric, makes it look at little softer.
How much you want to pad your embroidery is a personal choice. If you are framing stumpwork or metal thread work for example, you might like a little thicker padding to absorb the bulkiness of wires and heavy threads on the back so that they don't create lumps on the right side of the piece. For crewelwork a single layer of felt or thin wadding is fine.
If you are planning to use ready-made frame you can use the backing board from the frame as a template. If your are going to take the piece to the framer, make sure you have enough margin around the embroidery for the mat-board to overlap.
2. Cover the card with wadding or felt. Apply glue around the edges and across the centre of the card and press it onto your wadding - then trim it to size. I find it much easier and quicker doing it this way than cutting it to size and then gluing it in place.
3. Mark the centre along each side of the embroidered piece and place it with the wrong side facing up on a padded surface - I use a piece of blanketing covered with a light coloured tea towel. Then place the padded card over the fabric with the padding towards the fabric and aligning the centre lines and marks.
4. Thread a firm, strong thread such as a perle 8 into a needle. I use it straight from the ball to begin with.
As you lace towards one edge, make sure the grain of the fabric is straight along the edges. The lacing should be firm, but will not be really taut at this point. When you reach the side, secure the thread.
6. Next, cut the thread from the ball so that it is really long - you don't want to have to join it part way. Too long is better than too short and you will be surprised just how much thread you need. Lace to the other side as before and temporarily secure the thread.
7. Turn the piece over to check that it is neatly centred. (I forgot to do that and when I turned the finished piece, I thought it was sitting too low and I had to cut the lacing and start all over again).
When you are happy with the position, begin to firm up the lacing. It is a little bit like tightening shoe laces - start at the side that is secured and use your index and middle finger to pick up and tighten every second line of lacing, 'walking' your fingers across the back. Tighten the thread when you reach the opposite side.
You might need to do this a couple of times to get the lacing taut and even. It should be firm but not so tight it stretches the fabric and even worse, bends the card.
There is no need to mitre these corners as they will be covered by the frame or mat, but they should still be sharp, neat and flat. I use a ruler, slide it between the folded edges and use it to push the fabric taut and flat.