The diagonally angled panels on these may cause solid boning to twist if they curve to the side too much. If you already have flat boning, lay it over line and press it down over the whole length. If it seems to lie flat and stay over the line it's probably ok. Now each panel must be marked with a grain line. This will be used to orient the pattern piece on the fabric when you transfer the pattern.
Most patterns use a vertical grain line, but for a corset the horizontal grain is what is crucial.
If you already marked the waistline do it just above this. If you didn't mark the waistline, begin by placing the tape at the smallest part of the waist on the side. Then bring the tape to the front, and then around the back, keeping line perfectly horizontal. At the front the line may be above the smallest part of the waist, and it may be below the smallest part of the waist in back. Finally, mark the top and bottom matching lines.