I am currently making a pair of tartan check trousers from cloth that was cut at the bespoke shop.
I sewed the cloth into two separate trouser legs. I then go on to press them but because this particular pair has a raised side seam I have to press them differently. Usually with other trousers you would press the seam open but with this pair I have to press the back in lay on to the top inlay.
I leave out some extra cloth on the surface which we call a lip; this allows the seams to overlap creating what we call a raised seam.
Then I put the tacks in the pocket at the top and bottom and I stitch the whole way down the length of the side seam about 3/8 of an inch in to hold it in place so it doesn’t open again.