I obviously left out the middle bit where you put your new material on!
Do follow the FAQ guidance there, esp. about (i) getting all the cr@ppy foam residue off, (ii) getting a really good glue (and let us know if you find one that really works!) and (iii) not getting material that is too thick. It needs to be pretty thin or it will never go back in the strip above the windscreen. Other places may also be tight but that is the most obvious one.
Other tips. If I were doing it again (heaven forbid! (seriously it's not as bad as all that but it is time-consuming)) with more time, I would spend longer than I did restoring strength to the board. I might well consider painting or varnishing it before re-covering. If you could get something smooth that was stickily soaked into the terrible cardboardy stuff it would, I feel, be a more secure base for the glued material.
If using a patterned lining material
, take extra care to get it as straight as you can. It annoys me that mine is slightly off.
(PS Apols for the state of my hands! Been doing filthy and abrasive things to the other car. Manicure next week, maybe, if anyone would like to start a fund...)