The saddle flaps are the biggest piece so I usually start with them. I copy the bottom part of the flap directly from my drawing, add a bit in the middle to accommodate the seat area, and then cut the whole thing out and place it on the model.
From here on in, it's just a lot of trial and error. Since I didn't like the angle of the flaps when they were placed on the model, I cut them in half and reattached the pieces so they would hang straighter. I keep making adjustments until the piece looks right.
The next step is to move on to a related piece. I have decided this saddle will look just like a normal English saddle on the underside, so that means it will have a second, slightly smaller flap and panels. To make sure the pieces will fit together well, I temporarily attach them with glue stick . The glue stick makes a nice temporary bond, but it's still easy to pull things apart
so that you can make adjustments.In this picture you can see that I removed the panel and am now going to trim it along the pencil lines.
When I'm finally satisfied with the pattern, I trace each piece onto cardstock and cover one side with packing tape. This results in a nice sturdy pattern that holds up well over repeat uses. I used to put tape on both sides, but I've found that I like being able to write notes to myself directly on the pieces as I assemble the saddle. The skirt piece below comes from my pony dressage pattern. I don't make that type of saddle very often, but the next time I do I will know exactly what pieces need fixing before I start!