First I glued the tree on.
Next came the stirrups. (I have forgotten this step in the past and I have had to remove the seat of a saddle just to add stirrups).
Next I glued the seat onto the lower skirt. It is a very good idea to measure both sides of the seat to make sure it is not only centered behind the horn in the front, but also centered in the back. Repeat after me, "No crooked saddles". Fixing crookedness is way harder than making sure it's not crooked in the first place.
And while I was putting this saddle together, I noticed a ominous scratching sound at my window. All thanks to this little guy. I've named him Scratchy, but I don't know if he'll be back.