Second, I used flat sequins. While it was extremely easy to make this tissue box with flat sequins, the completed product just doesn't have
the shimmering quality that I had intended when I started out. So now I'm using faceted sequins. They are more difficult to work with, but the end product is so much better.
Third, I built the tissue box cover out of mesh before I started sewing on the sequins. This made it very difficult to get into the corners. Plus it was a hassle just due to the 3-dimensional shape. Now I'm sewing each face of the tissue box cover individually, and then sewing them all together at the end.
Lastly, I learned some smaller lessons. How to tie my knots securely, what order to sew the sequins on, etc.
I am extremely happy with how it looks in the end, but I could have saved a lot of time and money if I had known these lessons beforehand!