On my new Lady Grey jacket, I used an allover fusible stabilizer, Gridweft, on my loosely woven fabric. This is working great to keep the fabric from sagging, and it gives the jacket a bit of structure, but for the areas of a jacket that are typically interfaced, it is not enough. For those areas, I'm using an additional midweight fusible. Rather than cut all the individual pieces (back, fronts, side backs and fronts, and different sleeve pieces), I cut the interfacing after constructing most of my shell.
The fronts required a bit more finesse since I needed to consider the roll line of the lapels. I fused my pieces up to the roll line...
...then flipped the lapel back and fused that area, allowing the interfacing to fold around the roll line.
Here it is all fixed. Certainly not couture techniques, but I'm ok with that. :-)
I also cut pieces for the upper sleeves, just to make sure they don't collapse under the shoulder pads later.
For the undercollar, I used the same basic premise as the lapel roll line to mould my neck shape.
After the interfacing was fused, I trimmed off 1/8th inch around the edge of the undercollar.
You can see how the undercollar is now a smidge smaller than the upper collar piece (cut from the same pattern piece originally)
After it is pinned and sewn up, though...
... the seam lays nicely on the undercollar side.