I would cut out pretty huge pieces of the show so that the segments I did to, I could do to their fullest extent. I would try to take the tact that the stuff we don't see from the books is still happening in this world, we just are not telling that story. Like I would cut out the Iron Islands storylines, but I would assume all that shit still happens. For instance, we hear Balon dies and it is unknown who will succeed him. Then later on in Kings Landing, we get word Ironborn ships are attacking. If something turns out to be vitally important to the future, include it, if not, cut the the chase with its implications. It could be handled in % minutes- an Asha scene where she is talking to her lover about how she has a husband and the crows eye wants her dead, right before Stannis takes deepwood. I would cut out nearly all of the Dorne stuff, but not the characters. I wouldn't add anything just to keep actors in the show even when they don't have anything to do. I certainly wouldn't add battles or make small battles into huge battles, or turn wights into cgi skeletons. Thats wasteful imo. So when Stannis is missing until he goes to the wall, he is missing. Theon is missing, etc. If we are cutting Aegon, I don't really know where that story is going so I cant say. Quentyn can still be there, but we only see him from Dany's pov. She is established in Mereen, some guy snuck his way over there to say what he says, it goes bad, then we see the dragon scene.
I would protect the stories of Jon Snow/the North/Stannis, Dany/Mereen, Tyrion and Kings Landing/Cercei so they can be told fully. Tyrion's can be shortened if Aegon can be removed but like I said, I don't know the implications.
Lets not forget that no one forced D&D to shorten AFFC/ADWD to one season. I like those books a lot and would have adapted the main characters stories as closely as Season 2,3 adapted the material. I feel like that would have been really great television, they are fascinating stories and it is that which makes ASOIAF great imo, not the episode 9 battles. Seriously episode 9 was not worth having literally nothing happen the previous 8 episodes on the wall so much so that you have to invent your own terrible stories (crasters) to fill in time. Sorry, but I kind of have very little faith in D&D. When I see the Elio and Linda videos, I usually agree with them as far as the show except when it comes to Stannis. I am a huge Stannis fan and I just wish that the ADWD Stannis/the Wall/the North storyline was adapted closer than we are going to get. This turned into another rant. The end.