First thing to do is by the time he officially steps into the role he’d have informed the club of who he wants to bring in player wise and his back room staff would also already be in place to start the same day as Ten Hag does himself.
Secondly I expect Ten Hag and Rangnick to have been in constant conversation from now about who needs to leave and the club move on those not needed that are under contract (Henderson, Bailly, Jones, Tuanzebe, Williams, Matic, Pereira, Chong and Martial) and release those that aren’t under contract (Dalot, Pogba, Lingard, Mata and Cavani) so the decks are cleared.
Thirdly I expect a style of play and tactical methods to be instilled into the club that goes from the first team through to the under 23’s and into the academy teams so players at all levels are all on the same wave length and anyone stepping up is already up to speed with how we play and their specific role.
Fourthly my expectations would be for us to get a top four place so we’re back in the Champions League (although we mathematically can get it this season we need a miracle) and then making progress going into Ten Hag’s second season, with the players we have and how we know they CAN play top four is bare minimum.