First place to start is getting the sewn seam lined up on the panel straight, work the sides and then the top/bottom last. Usually was not any glue applied originally to the face of the panel, all on the back side.
For the ash tray opening, cut an X pattern and fold the 4 ears under.
Observe the original cover if you still have it to see how the corners and curves were trimmed to even out wrinkles.
A heat gun would also be good to use for stretching.
