I'm making a new Halloween corset, so I thought this would be the perfect chance to go over the steps of putting a corset together. I'm using a tested pattern so I didn't need to fit a mock-up.
I cut the pattern out of the fashion fabric and a khaki twill. Then I pinned the boning channels to the twill that would go between the seams:
I placed these channels from past experience, but in general you want a channel every 2-3" (remember there will also be boning on each seam). Also, if you have a problem with tummy pooch angling the boning slightly towards the center on the front and side front will help keep it in.
After sewing all the foundation boning I layered each piece with its corresponding fashion fabric piece and then sewed all the seams. This is before I ironed any of them. Since none of the seams cross each other you can wait until the end to press them all (although sometimes they're placed so closely together it can be difficult if you don't have a sleeve board).
I had to stop here because I haven't picked a fabric for the external boning channels yet (Black or Red? I'm so torn!). Here's a fun pic of the outside right now though: